Through the Smokescreen

For many years I was lucky enough to teach in a cancer biology course for third year natural science and medical students. Quite a few of those guys would already be eyeing up research careers and, within just a few months, some might be working on the very topics that came up in lectures. Nothing went down better, therefore, than talking about a nifty new method that had given easy-to-grasp results clearly of direct relevance to cancer.

Three cheers then for Mikhail Denissenko and friends who in 1996 published the first absolutely unequivocal evidence that a chemical in cigarette smoke could directly damage a bit of DNA that provides a major protection against cancer. The compound bound directly to several guanines in the DNA sequence that encodes P53 – the protein often called ‘the guardian of the genome’ – causing mutations. A pity poor old Fritz Lickint wasn’t around for a celebratory drink – it was he, back in the 1930s, that first spotted the link between smoking and lung cancer.

This was absolutely brilliant for showing how proteins switched on genes – and how that switch could be perturbed by mutations – because, just a couple of years earlier, Yunje Cho’s group at the Memorial Sloan-Kettering Cancer Center in New York had made crystals of P53 stuck to DNA and used X-rays to reveal the structure. This showed that six sites (amino acids) in the centre of the P53 protein poked like fingers into the groove of double-stranded DNA.

x-ray-picCentral core of P53 (grey ribbon) binding to the groove in double-stranded DNA (blue). The six amino acids (residues) most commonly mutated in p53 are shown in yellow (from Cho et al., 1994).

So that was how P53 ‘talked’ to DNA to control the expression of specific genes. What could be better then, in a talk on how DNA damage can lead to cancer, than the story of a specific chemical doing nasty things to a gene that encodes perhaps the most revered of anti-cancer proteins?

The only thing baffling the students must have been the tobacco companies insisting, as they continued to do for years, that smoking was good for you.

And twenty-something years on …?

Well, it’s taken a couple of revolutions (scientific, of course!) but in that time we’ve advanced to being able to sequence genomes at a fantastic speed for next to nothing in terms of cost. In that period too more and more data have accumulated showing the pervasive influence of the weed. In particular that not only does it cause cancer in tissues directly exposed to cigarette smoke (lung, oesophagus, larynx, mouth and throat) but it also promotes cancers in places that never see inhaled smoke: kidney, bladder, liver, pancreas, stomach, cervix, colon, rectum and white blood cells (acute myeloid leukemia). However, up until now we’ve had very little idea of what, if anything, these effects have in common in terms of molecular damage.

Applying the power of modern sequencing, Ludmil Alexandrov of the Los Alamos National Lab, along with the Wellcome Trust Sanger Institute’s Michael Stratton and their colleagues have pieced together whole-genome sequences and exome sequences (those are just the DNA that encode proteins – about 1% of the total) of over 5,000 tumours. These covered 17 smoking-associated forms of cancer and permitted comparison of tobacco smokers with never-smokers.

Let’s hear it for consistent science!

The most obvious question then is do the latest results confirm the efforts of Denissenko & Co., now some 20 years old? The latest work found that smoking could increase the mutation load in the form of multiple, distinct ‘mutational signatures’, each contributing to different extents in different cancers. And indeed in lung and larynx tumours they found the guanine-to-thymine base-pair change that Denissenko et al had observed as the result of a specific chemical attaching to DNA.

For lung cancer they concluded that, all told, about 150 mutations accumulate in a given lung cell as a result of smoking a pack of cigarettes a day for a year.

Turning to tissues that are not directly exposed to smoke, things are a bit less clear. In liver and kidney cancers smokers have a bigger load of mutations than non-smokers (as in the lung). However, and somewhat surprisingly, in other smoking-associated cancer types there were no clear differences. And even odder, there was no difference in the methylation of DNA between smokers and non-smokers – that’s the chemical tags that can be added to DNA to tune the process of transforming the genetic code into proteins. Which was strange because we know that such ‘epigenetic’ changes can occur in response to external factors, e.g., diet.

What’s going on?

Not clear beyond the clear fact that tissues directly exposed to smoke accumulate cancer-driving mutations – and the longer the exposure the bigger the burden. For tissues that don’t see smoke its effect must be indirect. A possible way for this to happen would be for smoke to cause mild inflammation that in turn causes chemical signals to be released into the circulation that in turn affect how efficiently cells repair damage to their DNA.

raleighs_first_pipe_in_england-jpeg

Sir Walt showing off on his return                         to England

Whose fault it is anyway?

So tobacco-promoted cancers still retain some of their molecular mystery as well as presenting an appalling and globally growing problem. These days a popular pastime is to find someone else to blame for anything and everything – and in the case of smoking we all know who the front-runner is. But although Sir Walter Raleigh brought tobacco to Europe (in 1578), it had clearly been in use by American natives long before he turned up and, going in the opposite direction (à la Marco Polo), the Chinese had been at it since at least the early 1500s. To its credit, China had an anti-smoking movement by 1639, during the Ming Dynasty. One of their Emperors decreed that tobacco addicts be executed and the Qing Emperor Kangxi went a step further by beheading anyone who even possessed tobacco.

And paying the price

And paying the price

If you’re thinking maybe we should get a touch more Draconian in our anti-smoking measures, it’s worth pointing out that the Chinese model hasn’t worked out too well so far. China’s currently heading for three million cancer deaths annually. About 400,000 of these are from lung cancer and the smoking trends mean this figure will be 700,000 annual deaths by 2020. The global cancer map is a great way to keep up with the stats of both lung cancer and the rest – though it’s not for those of a nervous disposition!

References

Denissenko, M.F. et al. ( (1996). Preferential Formation of Benzo[a]pyrene Adducts at Lung Cancer Mutational Hotspots in P53.Science 274, 430–432.

Cho, Y. et al. (1994). Crystal Structure of a p53 Tumor Suppressor-DNA Complex: Understanding Tumorigenic Mutations. Science, 265, 346-355.

Alexandrov, L.D. et al. (2016). Mutational signatures associated with tobacco smoking in human cancer. Science 354, 618-622.

Bigger is Better

“Nonsense!” most males would cry, quite logically, given that we spend much of our time trying to persuade the opposite sex that size doesn’t matter. But we want to have it both ways: in the macho world of rugby one of the oldest adages is that ‘a good big ’un will always beat a good little ’un’.  Beethoven doubtless had a view about size – albeit unrecorded by history – but after he’d written his Eroica symphony, perhaps the greatest revolutionary musical composition of all, his next offering in the genre was the magical Fourth – scored for the smallest orchestra used in any of his symphonies. And on the theme of small can be good, the British Medical Journal, no less, has just told us that if we cut the size of food portions and put ’em on smaller plates we’ll eat less and not get fat!

Is bigger better?

Is bigger better?

All of which suggests that whether bigger is better depends on what you have in mind. Needless to say, in these pages what we have in mind is ‘Does it apply to cancer?’ – that is, because cancers arise from the accumulation in cells of DNA damage (mutations), it would seem obvious that the bigger an animal (i.e. the more cells it has) and the longer it lives the more likely it will be to get cancer.

Obvious but, this being cancer, also wrong.

Peto’s Paradox

The first person to put his finger on this point was Sir Richard Peto, most famous for his work with Sir Richard Doll on cancer epidemiology. It was Doll, together with Austin Bradford Hill, who produced statistical proof (in the British Doctors’ Study published in 1956) that tobacco smoking increased the risk of lung cancer. Peto joined forces with Doll in 1971 and they went on to show that tobacco, infections and diet between them cause three quarters of all cancers.

Whenever this topic comes up I’m tempted to give a plug to the unfortunate Fritz Lickint – long forgotten German physician – who was actually the first to publish evidence that linked smoking and lung cancer and who coined the term ‘passive smoking’ – all some 30 years before the Doll study. Lickint’s findings were avidly taken up by the Nazi party as they promoted Draconian anti-smoking measures – presumably driven by the fact that their leader, Gröfaz (to use the derogatory acronym by which he became known in Germany as the war progressed – from Größter Feldherr aller ZeitenGreatest Field Commander of all Time) was a confirmed non-smoker. Despite his usefulness, Lickint’s political views didn’t fit the ideology of the times. He lost his job, was conscripted, survived the war as a medical orderly and only then was able to resume his life as a doctor – albeit never receiving the credit he deserved.

Returning to Richard Peto, it was he who in 1975 pointed out that across different species the incidence of cancer doesn’t appear to be linked to the number of cells in animal – i.e. its size.   He based his notion on the comparison of mice with men – we have about 1000 times the number of cells in a mouse and typically live 30 times as long. So we should be about a million times more likely to get cancer – but in fact cancer incidence is another of those things where we’re pretty similar to our little furry friends. That’s Peto’s Paradox.

It doesn’t seem to apply within members of the same species, a number of surveys having shown that cancer incidence increases with height both for men and women. The Women’s Health Initiative found that a four inch increase in height raised overall cancer risk by 13% although for some forms (kidney, rectum, thyroid and blood) the risk went up by about 25%. A later study found a similar association for ovarian cancer: women who are 5ft 6in tall have a 23% greater risk than those who only make it to 5 feet. A similar risk links ovarian cancer to obesity (i.e. a rise in body mass index from 20 (slim) to 30 (slightly overweight) puts the risk up by 23%). Statistically sound though these results appear to be, it’s worth nothing that, as my colleague Paul Pharoah has pointed out, these risk changes are small. For example, the ovarian cancer finding translates to a lifetime risk of about 16-in-a-1000 for shorter women going up to 20-in-a-1000 as they rise by 6 inches.

It’s true that there may be a contribution from larger animals having bigger cells (whale red blood cells are about twice as big as those of the mouse) that divide more slowly but at most that effect seems small and doesn’t fully account for the fact that across species the association of size and age with cancer breaks down: Peto’s Paradox rules – humans are much more likely to get cancer than whales.

What did we know?

Well, since Peto picked up the problem, almost nothing about underlying causes. The ‘almost’ has been confined to the very small end of the scale and we’ve already met the star of the show – the naked mole rat – a rather shy chap with a very long lifespan (up to 30 years) but who never seems to get cancer. In that piece we described the glimmerings of an explanation but, thanks to Xiao Tian and colleagues of the University of Rochester, New York we now know that these bald burrowers make an extraordinarily large version of a polysaccharide (a polymer of sugars). These long strings of glucose-like molecules (called hyaluronan) form part of the extracellular matrix and regulate cell proliferation and migration. They’re enormous molecules with tens of thousands of sugars linked together but the naked mole rat makes versions about four times larger than those of mice or humans – and it seems that these extra-large sugar strings restrict cell behaviour and block the development of tumours.

Going up!

Our ignorance has just been further lifted with two heavyweight studies, one from Lisa Abegglen, Joshua Schiffman and chums from the University of Utah School of Medicine who went to the zoo (San Diego Zoo, in fact) and looked at 36 different mammalian species, ranging in size from the striped grass mouse (weighing in at 50 grams) to the elephant – at 4,800 kilogram nearly 100,000 times larger. They found no relationship between body size and cancer incidence, a result that conforms to Peto’s paradox. Comparing cancer mortality rates it transpires that the figure for elephants is less than 5% compared with the human range of 11% to 25%.

107 final pic

Cancer incidence across species by body size and lifespan. A selection of 20 of the 36 species studied is shown. Sizes range from the striped grass mouse to the elephant. As the risk of cancer depends on both the number of cells in the body and the number of years over which those cells can accumulate mutations, cancer incidence is plotted as a function of size (i.e. mass in grams × life span, years: y axis: log scale). Each species is represented by at least 10 animals (from Abegglen et al., 2015).

It can be seen at a glance that cancer incidence is not associated with mass and life span.

The Tasmanian devil stands out as a remarkable example of susceptibility to cancer through its transmission by biting and licking.

How does Jumbo do it?

In a different approach to Peto’s Paradox, Michael Sulak, Vincent Lynch and colleagues at the University of Chicago looked mainly at elephants – more specifically they used DNA sequencing to get at how the largest extant land mammal manages to be super-resistant to cancer. In particular they focused on the tumor suppressor gene P53 (aka TP53) because its expression is exquisitely sensitive to DNA damage and when it’s switched on the actions of the P53 protein buy time for the cell to repair the damage or, failing that, bring about the death of the cell. That’s as good an anti-cancer defence as you can imagine – hence P53’s appellation as the ‘guardian of the genome’. It turned out that elephants have no fewer than 20 copies of P53 in their genome, whereas humans and other mammals have only one (i.e. one copy per set of (23) chromosomes). DNA from frozen mammoths had 14 copies of P53 but manatees and the small furry hyraxes, the elephant’s closest living relatives, like humans have only one.

The Utah group confirmed that elephants have, in addition to one normal P53 gene, 19 extra P53 genes (they’re actually retrogenes – one type of the pseudogenes that we met in the preceding post) that have been acquired as the animals have expanded in size during evolution. Several of these extra versions of P53 were shown to be switched on (transcribed) and translated into proteins.

Consistent with their extra P53 fire-power, elephant cells committed P53-dependent suicide (programmed cell death, aka apoptosis) more frequently than human cells when exposed to DNA-damaging radiation. This suggests that elephant cells are rather better than human cells when it comes to killing themselves to avoid the risk of uncontrolled growth arising from defective DNA.

More genes anyone?

Those keen on jumping on technological bandwagons may wish to sign up for an extra P53 gene or two, courtesy of genetic engineering, so that bingo! – they’ll be free of cancers. Aside from the elephant, they may be encouraged by ‘super P53’ mice that were genetically altered to express one extra version of P53 that indeed significantly protected from cancer when compared with normal mice – and did so without any evident ill-effects.

We do not wish to dampen your enthusiasm but would be in dereliction of our duty is we did not add a serious health warning. We now know a lot about P53 – for example, that the P53 gene encodes at least 15 different proteins (isoforms), some of which do indeed protect against cancer – but there are some that appear to act as tumour promoters. In other words we know enough about P53 to realize that we simply haven’t a clue. So we really would be playing with fire if we started tinkering with our P53 gene complement – and to emphasise practicalities, as Mel Greaves has put it, we just don’t know how well the elephants’ defences would stack up if they smoked.

Nevertheless, on the bright side, light is at long last beginning to be shed on Peto’s Paradox and who knows where that will eventually lead us. Meanwhile Richard Peto’s activities have evolved in a different direction and he now helps to run a Thai restaurant in Oxford, a cuisine known for small things that pack a prodigious punch. Bit like Beethoven’s Fourth you could say.

a-gem-of-a-find-in-oxford

References

Peto, R. et al. (1975). Cancer and ageing in mice and men. British Journal of Cancer 32, 411-426.

Doll, R. and Peto, R. (1976). Mortality in relation to smoking: 20 years’ observations on male British doctors. Br Med J. 2(6051):1525–36.

Maciak, S. and Michalak, P. (2015). “Cell size and cancer: A new solution to Peto’s paradox?”. Evolutionary Applications 8: 2.

Doll, R. and Hill, A.B. (1954). “The mortality of doctors in relation to their smoking habits”. BMJ 328 (7455): 1529.

Doll, R. and Hill, A.B. (November 1956). “Lung cancer and other causes of death in relation to smoking; a second report on the mortality of British doctors”. British Medical Journal 2 (5001): 1071–1081.

Tian, X. et al. (2013). High-molecular-mass hyaluronan mediates the cancer resistance of the naked mole rat. Nature 499, 346-349.

Abegglen, L.M., Schiffman, J.D. et al. (2015). Potential Mechanisms for Cancer Resistance in Elephants and Comparative Cellular Response to DNA Damage in Humans. JAMA. doi:10.1001/jama.2015.13134.

Sulak, M., Lindsey Fong, Katelyn Mika, Sravanthi Chigurupati, Lisa Yon, Nigel P. Mongan, Richard D. Emes, Vincent J. Lynch, V.J. (2015). TP53 copy number expansion correlates with the evolution of increased body size and an enhanced DNA damage response in elephants. doi: http://dx.doi.org/10.1101/028522.

García-Cao, I. et al. (2002). ‘Super p53’ mice exhibit enhanced DNA damage response, are tumor resistant and age normally. EMBO Journal 21, 6225–6235.

Cancer Genetics: Never Black or White

The National Heath Service occupies a uniquely revered place in the psyche of the British people – as indeed it should, the concept of free, first rate health care available when required being one of the hallmarks of civilization. Founded in 1948, the NHS has continued to this day to fulfill its remit with astonishing efficiency in the face of demands beyond comprehension sixty years ago, as both the size of the population and life expectancy have increased and medical practice has been transformed by technical advances. Even so, there is one area in which there is a surprising shortfall in the performance of the NHS when compared with most other European countries or with the USA – cancer survival rates.

We’re behind you!!

Broadly speaking, the latest findings of a massive study (called CONCORD-2, a long-term global comparison of cancer survival) show 5-year cancer survival rates in the UK for 2005 to 2009 to have been worse than they were in many European countries at least a decade earlier. “Shameful” cried Macmillan Cancer Support – rarely a helpful response but you have to concede it’s scarcely grounds for an outbreak of British smugness. More to the point, Cancer Research UK insisted the gulf was often linked to deprivation, i.e. patients in poorer areas tend to live unhealthy lifestyles so they are more susceptible and likely to be diagnosed later. This refers to what has become known as the postcode (zipcode) lottery whereby the chances of being diagnosed early and surviving various forms of cancer differ significantly (meaning as much as two-fold!) across the UK. Further contributions come from general practitioners missing the early signs of cancer, adding to the delay in referral, together with variable standards of treatment.

And the answer is?

But hang on! None of this actually explains why these problems should be more acute in the UK than in, say, France or Finland who presumably have their share of the poor and incompetent. So what might be different in the UK? Here’s my theory. Maybe it’s just us, the Jane & John Does lining up to become cancer patients. Dentists reckon they can pick Brits from Yanks just by peering into their oral cavities (Brits have cavities {ho ho} whereas Americans are perfect – tooth-wise that is). Why? Because we don’t care: we figure our bodies are non-maintenance machines – so we never dream of getting them serviced, that is, having regular check-ups – and when they do conk out we expect the wondrous NHS to fix it. To see if there’s any truth in this theory I conducted a meaningless, random poll in my department (featuring two Americans, one Finn, a Dutchman, two German ladies and a French girl – all from nations that do better than the UK) asking ‘how health aware are your countrymen compared with the British?’ Result? They’re all hypochondriacs compared to Brits whose default method is to avoid doctors until they’re at death’s door. So there we have it: it’s our fault and if we just looked after ourselves a bit better the UK would scrabble its way up the cancer survival league.

Sounds familiar?

Take the specific example of breast cancer. 81% of UK women diagnosed between 2005 and 2009 were alive five years later but in Sweden, France and Italy the rates range from 86 to 87%. This kind of gap is reminiscent of that in the USA between African American women and those of European descent – presently 79% versus 92 % – a disparity that has remained pretty constant over the last 40 years even though the survival rates of both groups have steadily risen (the overall USA survival rate for breast cancer is now 89%). Again the divide has been attributed to poverty and education level, together with lack of health insurance, so that detection is delayed and survival times shortened.

So it’s clear that multiple factors contribute to the variable treatment success rates but so far there’s no evidence that genetic differences play a part, for example, by giving rise to more aggressive forms of cancer.

A little more light in one corner

Breast cancers are an enormously varied set of diseases and as such they’re a challenge even to classify yet alone to treat. The recent rapid progress in DNA sequencing has led to a new genome-based classification system but there is still strong reliance on the traditional prognostic and predictive factors, notably what’s called hormonal status – meaning presence on the surface of the tumour cells of the protein receptors to which the hormones oestrogen and progesterone attach, together with the presence or otherwise of the human epidermal growth factor receptor 2 (HER2). One significant sub-group has no detectable levels of these proteins – they’re ‘triple negative’ – and they make up 10-15% of breast cancers (TNBCs). TNBCs are very aggressive cancers (poor prognosis), known for some years to disproportionally affect young women of African origin – it’s about twice as common in African Americans as in European Americans.

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The triple negative breast cancer survival rate dependence on race.

African-American women with TNBC have poorer survival rates than women of European descent (Dietze et al., 2015).

Step forward DNA sequencing – again!

What wasn’t known was anything by way of explanation of these epidemiological findings but from sequencing tumour DNA it has emerged that mutations in BRCA1 are present in most (69%) of TNBCs in women of European origin. Inherited mutations in BRCA1 are particularly associated with breast and ovarian cancers, as we explained in a recent item on Angelina Jolie (A Taxing Inheritance). But here’s a very odd thing: African-American women have a low incidence of BRCA1 mutations (less than 20%), despite the fact that they are relatively prone to TNBC.

What’s new?

Well, if BRCA1 isn’t doing the driving there must be other potent drivers for TNBC and the new genetic studies have given us one more piece in the molecular jigsaw of cancer. However, to take up Frances M. Visco’s point in a recent letter to The New York Times and one that I have made forcefully elsewhere (in Not another ‘Great Cancer Breakthrough’!!! and Gentlemen! For goodness’ sake …), this is not another ‘breakthrough’ yet alone a ‘great one.’ It won’t save lives until we identify what the other drivers are and come up with a therapeutic ploy to exploit our knowledge.

Right on cue, step forward Alex Swarbrick, Simon Junankar and colleagues from Sydney’s Garvan Institute of Medical Research who have just found that a protein called ID4 appears to control some TNBCs: it’s present at high levels in about half of all TNBCs. ID4 stands for ‘inhibitor of differentiation 4′ which means that it keeps cells in a state where they can continue to divide – a hallmark of cancer.

So now it’s over to the lads from down under to do the difficult bit and come up with an inhibitor of ID4 – and to show that it works to stop TNBCs in their tracks.

References

Allemani, C. et al., (2015). Global surveillance of cancer survival 1995-2009: analysis of individual data for 25 676 887 patients from 279 population-based registries in 67 countries (CONCORD-2). Lancet 385, 977-1010.

Dietze, E. et al., (2015). Triple-negative breast cancer in African-American women: disparities versus biology. Nature Reviews Cancer 15, 248–254.

Junankar, S. et al., (2015). ID4 controls mammary stem cells and marks breast cancers with a stem cell-like phenotype. Nature Communications 6, Article number: 6548 doi:10.1038/ncomms7548.

 

A Taxing Inheritance

The centenary of the beginning of the First World War prompted me, as perhaps many others, to reflect on how successive generations have done since then in terms of what they’ve bequeathed to their offspring. I didn’t need to think for too long though, to find myself muttering ‘Thank heavens for science’—because most of the rest is a pretty dismal chronicle. I know, not all technological advances in the past one hundred years have been a cause of unrestrained joy but many of them transformed life in the most wonderful ways. Would that we could point to such success in other fields.

Our best defence may be to aver: “Man cannot control the current of events. He can only float with them and steer”, a saying attributed to Otto von Bismarck. If the ‘Iron Chancellor’ actually did utter those words it seems to me he was being coy beyond belief. He is, after all, generally credited with unifying Germany, seeing off the last French monarch (Napoleon III) and establishing the peaceful domination of Europe by the German Empire that lasted until long after his death—and setting up the first welfare state along the way. “The main thing is to make history, not to write it” sounds much more like Bismarck in full and frank mode.

Nature and Nurture

One form of history that we do write but indeed we cannot control comes in the form of the genetic material that we pass to the next generation. We’re all familiar with some of this legacy because we literally see it in physical resemblances and other attributes between parents and children (“He’s got his Mum’s eyes”) or shared by siblings (“Jack and Jill are wonderful musicians”). They’re shared because large chunks of the genetic code (i.e. DNA) are identical between the individuals concerned. But if conserved DNA makes for similarities, what of the differences—the fact that our parents and brothers look different to all the seven thousand million other people on the planet? Our unique features come from variations in the genetic code—odd changes in the units (bases) of DNA scattered through our genome. Called SNPs (pronounced ‘snips’ for single nucleotide polymorphisms), they’re what make the differences between us. In other words, a SNP is a difference in a single nucleotide—A, T, C or G—within a stretch of DNA sequence that is otherwise identical between two individuals. For example, you have AAGCCTA whereas I have AAGCTTA. These genetic variations that make individuals different are the basis of DNA fingerprinting.

There’s about three million SNPs scattered throughout the human genome (so, on average, you’d come across one in every 1,000 bases if you scanned your DNA from beginning to end) and they’re what makes each of us unique. Within ethnic groups common patterns of such variants confer characteristics (dark skin/light skin, tall/short, etc) and, with that in mind, you might guess that there will also be variants that make such groups more (or less) susceptible to diseases.

Of course, there’s an endless debate about the border between our genetic inheritance and how the world we experience makes us what we are—how much of Jack and Jill’s precocious talent is because Mum and Dad made them practice twelve hours a day from age five? Fortunately we can ignore nurture here and stick to genes because we’re trying to pin down the good and the bad of our genetic legacy.

What’s all this got to do with cancer?

A good bit is that we’re distinct from everyone else but still share family features. However, our genetic baggage may also contain some unwanted freebies—the most potent of which can give a helping hand to a variety of diseases, including cancers. Cancers are caused by damage to DNA—a build-up of changes, i.e. mutations, that affect the activity of proteins critically involved in controlling cell growth. For most cancers (90%) these mutations accumulate over the lifetime of the individual—they’re called “somatic mutations”—so you can’t blame anyone but yourself and Lady Luck. But about 10% get a kind of head start when someone is born with a key mutation. That is, the mutated gene came from either egg or sperm (so it’s a germline mutation). This effect gives rise to cancers that “run in families”: a critical mutation is passed from generation to generation so that children who inherit it have a greatly increased risk of developing cancer. Two of the most common cancers that can come in hereditary form are those of the breast and bowel.

Steeplechase

A mutational steeplechase leads to cancer. Of the tens of thousands of mutations that accumulate over time in a cancer cell, a small number of distinct “drivers” make the cancer develop (four are shown as Xs). Almost all mutations arise after birth, but about one in every ten cancers start because a person is unfortunate enough to be born with a mutation: they are already one jump ahead and are much more likely to get cancer than those born with a normal set of genes. The rate at which mutations arise is increased by exposure to carcinogens, e.g., in tobacco smoke.

Breast cancer is about twice as common in first-degree relatives of women with the disease as it is in the general population (you’re a first degree relative if you’re someone’s parent, offspring, or sibling). About 5% of all female breast cancers (men get the disease too but very rarely—about 1% of all breast cancers) arise from inherited mutations. In the 1990s two genes were identified that can carry such mutations. These are BRCA1 and BRCA2 and their abnormal versions can increase the lifetime risk of the disease to over 50%, compared with an average of about 10%. Since then heritable mutations in some other genes have also been shown to increase the risk.

Angelina Jolie

Angelina Jolie

A star turn

Breast cancer genetics came under the spotlight with the much-publicised saga of Angelina Jolie, the American film actress. Jolie’s mother and maternal grandmother had died of ovarian cancer and her maternal aunt from breast cancer—a family history that persuaded Jolie to opt for genetic testing that indeed revealed she was carrying a mutation in BRCA1 (BRCA1 and BRCA2 mutations account for about 10% of breast cancers and 15% of ovarian cancers). For Jolie the associated lifetime risk of breast cancer was estimated as 87%, prompting her to have a preventative double mastectomy, thereby reducing her risk to less than 5%. The months after she revealed her story saw the “Angelina effect”, a doubling in the number of women being referred for genetic testing for breast cancer mutations.

What’s all this got to do with SNPs?

The story so far is of the one in ten cancers that get kicked off by a powerful, inherited mutation that changes the action of the affected protein—the BRCAs being the best-known examples. However, the BRCAs and other known mutated genes account for only about 25% of familial breast cancers, meaning that for three quarters of cases the genetic cause remains unknown. And yet we know there is an inherited (genetic) cause simply because of the generational thread. Which brings us back to those other, more subtle tweaks to DNA that we mentioned—SNPs—alterations that don’t directly affect proteins, so they’re often called variants to distinguish them from mutations.

It seems very likely that the missing culprits are indeed SNPs—lots of them. These DNA variants each make a contribution so small that on its own would have no detectable effect on the chances that the carrier will get cancer. Their impact comes from a cumulative effect. They’re like pieces of straw, individually easily bent or broken but put a dozen of them together and you have a rope. Thus combinations of individually insignificant SNPs can raise the risk of cancer by, say, 10%—not a massive increase but not negligible either. Twins who are genetically identical have similar risks of developing breast cancer, consistent with the idea that many variants, each having a very small effect, can combine to give a substantial increase in risk. Very slowly, by sequencing lots of genomes, these rare variants are being identified. Given that clusters of appropriate variants confer risk, people with the “other” variant have, in effect, a degree of protection against cancer.

And in our more distant relatives?

All this comes from the huge effort that has gone into finding genetic variants linked to one of the most common cancers but, unsurprisingly, almost all the attention has focused on European women. Not before time, someone has got round to looking for breast cancer variants in East Asians who, after all, make up over one fifth of all the people in the world. Cai Qiuyin and his colleagues at the Vanderbilt University School of Medicine compared the genomes of over 20,000 cancer cases from China, Japan and South Korea with a similar number of disease-free controls. After much selecting and comparing of sequences, three particular DNA variants consistently associated with significant cancer risk. The variants were much less common in European women, suggesting that as the DNA keyboard has been strummed by evolution, distinct patterns associated with breast cancer have emerged in diverse populations.

Just two problems then. First it’s a huge task to assemble the lists of runners (and as the Asian results show, they will differ between ethnic groups). But the real challenge is yet to come. Almost all of these variants (99.9%) don’t change the sequence of proteins (i.e. how the proteins work). What they do is exert subtle effects on, for example, how much RNA or protein is made from a DNA gene at any time. At the moment we have little understanding of how this works, yet alone ideas on how to intervene to change the outcome.

Although identifying the BRCA genes that help to drive breast and ovarian cancers was a giant breakthrough, we still have no effective therapy for countering their malign influences. The intervening twenty-five years of effort have brought us to a new era of revealing the more subtle effects of variants. But the price we pay for unveiling the complete picture is perceiving just how tough is the therapeutic challenge.

Reference

Qiuyin Cai, et al. (2014). Genome-wide association analysis in East Asians identifies breast cancer susceptibility loci at 1q32.1, 5q14.3 and 15q26.1. Nature Genetics 46, 886–890. doi:10.1038/ng.3041.

Risk Assessment

For UK readers a title that instantly raises the spectre of the ’Elf & Safety police and the annoyance, irritation and amusement generated by the seemingly ubiquitous injunctions of their minions. Even my department is not spared, the harbinger of warm weather invariably being an email reminding us that this is no reason for abandoning the rule that at all times we should wear a lab coat – though, to be fair, our local enforcer usually includes the cheeky inference that we retain the option of going naked underneath. Ah, The Joy of Science! ’E & S’s reputation comes, of course, from periodically making the headlines by banning a centuries-old tradition in some rustic backwater involving such fun activities as rolling cheeses down a hill.

Stuart Kettell and sprout

Stuart Kettell and sprout

Mind you, they’ve slipped up recently by allowing Stuart Kettell to push a Brussels sprout up Mount Snowdon with his nose. As that’s 3,560ft (vertically) he probably did lasting damage to his knees, to say nothing of his hooter, as well as inflicting grievous bodily harm on 22 sprouts (they wear out on the basalt, obviously). By his own admission, he’s probably mad – but he did at least raise some money for Macmillan Cancer Support.

 

But why are we bothered about assessing risk?

Setting the above entertainment to one side, estimating risk can be a really serious business and never more so than when it comes to cancer. It’s an especially contentious, long-running issue for breast cancer and both in Betrayed by Nature and more recently in Behind the Screen I tried to crystallize some clear guidelines from the vast amount of available info. In short these were: ignore commercial plugs for thermography – the only test to go for is mammography – i.e. X-ray imaging to find breast cancer before a lump can be felt. And the simple message you were relieved to read in BbN was that, whilst the matter is controversial, if you are offered screening, accept – but be aware that the method is not perfect. There’s a small risk that a cancer may be missed and a bigger chance that something abnormal but harmless will be picked up – a signal for intervention (by surgery and drugs) and that, in those cases, would be unnecessary.

And we’re revisiting this question?

Because there have been some recent contributions to the debate that might well have increased confusion and concern in equal measure for women who are desperately trying to make sense of it all. The most controversial of these comes from a panel of experts (The Swiss Medical Board) who reviewed the history of mammography screening – and recommended that the current programmes in Switzerland should be phased out and not replaced.

Needless to say, their report caused a furore, not only in Switzerland, with experts damning its conclusions as ‘unethical’ – mainly because they ran counter to the consensus that screening has to be a good thing.

So what did the Swiss Big Cheeses point out to get into such hot water? Their view after considering the cumulative evidence was that systematic mammography might prevent about one breast cancer death for every 1,000 women screened. However, two other things struck them. First, it was not clear that this result outweighed the disadvantages of screening – what are inelegantly referred to as the ‘harms’ – the detection and treatment of something ‘abnormal but harmless’ mentioned earlier. Second that, on the basis of a survey by American group, women had a grossly optimistic idea of the benefits of mammography.

Good versus bad

Two of the weightiest bits of evidence that led them to conclude that screening does more harm than good were studies that had combined several independent investigations – what’s called a meta-analysis – which is a way of increasing your sample size and hence getting a more meaningful answer. One of these (The Independent United Kingdom Panel on Breast Cancer Screening) pulled together 11 trials from which it emerged that women invited to screening had a reduction of about 20% in their risk of dying from breast cancer compared with controls who were not offered screening. So far so good. However, inevitably there were differences in methods between the trials, which made the UK Panel very cagey about drawing more specific conclusions but their best estimate was that, for every 10,000 UK women aged 50 years invited to screening for the next 20 years, 43 deaths from breast cancer would be prevented and 129 cases would be over-diagnosed. Over-diagnosis means detection of cancers that would never have been emerged during the lifetime of the individuals and these healthy women will be needlessly subjected to some combination of surgical interventions, radiotherapy and chemotherapy.

The second combined study is from The Cochrane Collaboration, the trials involving more than 600,000 women. Their review also emphasized the variation in quality between different studies and noted that the most reliable showed that screening did not reduce breast cancer mortality. However, less rigorous methods introduced bias towards showing that screening did reduced breast cancer mortality. In this sort of trial “less rigorous” relates particularly to the problem of ensuring that the two groups of subjects are truly randomized – i.e. that nothing influences whether a woman is assigned to receive screening mammograms or not. This is much harder than it sounds, mainly because human beings do the assigning so there is always a chance of either a genuine mistake or a flaw in the design of a particular study. One simple example of how the best laid plans … The consent form for a study specifically states that women are assigned, at random, to either the mammography or no mammography group. Women are then examined by a specially trained nurse. However, if these two steps are reversed, assignment may be biased by the findings of the examination. Precisely such a failure to adhere to a protocol has been revealed in at least one study.

Making the liberal assumption that screening reduces mortality by 15% and that over-diagnosis occurs at a rate of 30%, they estimated that for every 2000 women invited for screening over 10 years, one will avoid dying of breast cancer and 10 will be treated unnecessarily. In addition, false alarms will subject 200 women to prolonged distress and anxiety.

All of which explains why, taking everything into consideration, the Big Cheeses recommended that the Swiss abandon mammography screening.

MammogramWhat does the NHS say?

Actions speak louder than words and in the UK women aged 50 to 70 are invited for mammography screening every three years. By way of explanation, the NHS document (NHS breast screening: Helping you decide) says that for every 200 screened about one life is saved from breast cancer. The American Cancer Society recommends screening annually from age 40 – so it’s clear that Britain and the USA are firmly in favour.

You will have noted that the NHS figure of one saved for every 200 screened is seriously at odds with the findings summarized above and they don’t say where it comes from. However, they are clear about the critical point in saying “for every 1 woman who has her life saved from breast cancer, about three women are diagnosed with a cancer that would never have become life-threatening.”

Misplaced optimism

It will be obvious by now that attaching precise numbers to the effects of screening is next to impossible but the overall message is clear. At best screening yields a small reduction in breast cancer deaths but this comes with a substantially greater number of women who are treated unnecessarily – hence the Swiss position that it is ethically difficult to justify a public health program that does more harm than good.

It’s a bit difficult to assess just how knowledgeable women are about the benefits of mammography screening but one study that tried came up with some positively alarming pointers. A telephone survey of more than 4000 randomly chosen females over 15 years of age in the USA, the UK, Italy and Switzerland revealed that a substantial majority believed that (i) screening prevents or reduces the risk of getting breast cancer, (ii) screening at least halves breast cancer mortality, and (iii) 10 years of regular screening prevents 10 or more breast cancer deaths per 1000 women.

A clear conclusion?

Rates of breast cancer mortality are declining. Hooray! And the five-year survival rate in developed countries is now about 90%. Hooray again! It seems probable that this trend is more though improved treatments and greater awareness – leading to early detection – than because of screening. Nevertheless, all that doesn’t alter the fact that where women are offered the choice they need to be as well informed as possible. The weaknesses of the telephone survey are obvious but the implication that misconceptions are widespread indicates that we need to do much better at explaining the facts of mammography screening.

References

Biller-Andorno N. and Jüni P. (2014). Abolishing mammography screening programs? A view from the Swiss Medical Board. New England Journal of Medicine 370:1965-7.

Independent UK Panel on Breast Cancer Screening. (2012). The benefits and harms of breast cancer screening: an independent review. Lancet 380:1778-86.

Gøtzsche, P.C. and Jørgensen, K.J. (2013). Screening for breast cancer with mammography. Cochrane Database Syst Rev; 6:CD001877.

Domenighetti G, D’Avanzo B, Egger M, et al. (2003). Women’s perception of the benefits of mammography screening: population-based survey in four countries. Int J Epidemiol., 32:816-21.

What Took You So Long?

A long, long time ago – 25 years to be precise – I was lucky enough to work for a few months at The University of New England in Armidale, up on the Northern Tablelands of New South Wales. And jolly wonderful it was too. You could see grazing kangaroos from my lab window and I got to play grade cricket! To anyone who’ll listen I can still describe in vivid detail the scoring of my first run in Oz. We’d won the toss and … (that’s quite enough cricket, Ed).

Equally wonderful is the fact that, in part courtesy of The University of Queensland, I’m going again to Oz – this time to do what I didn’t manage then: visit all the major cities. We begin in Brisbane this week giving a lecture in the U of Q’s Global Leadership series (yes really!), explaining the biology of cancer to an audience of largely non-scientists – at least I hope I’ve got the right brief! We end up in Perth in May having, in between if I can stick the pace, given a variety of talks and seminars to the general public, to schools and to cancer research institutes in Sydney, Melbourne and Adelaide. How good is that? Being invited to warble on about one of your favorite subjects whilst touring Oz? Wow!

What’s new?

All of which makes you think a bit about Father Time and what has happened in the interim. Answer quite a lot, of course. Collapse of communism, collapse and resurgence of Australian cricket (that’s your last warning, Ed) and so on but we’re supposed to inform and enthuse about cancer here so how’s that faired, particularly in Australia? Well, in the year I first followed Captain Cook (watch it, Ed) onto the shore of Botany Bay about 60,000 Australians were diagnosed with cancers of one sort or another and some 30,000 died from these diseases. At that time one in three men and one in four women would be directly affected by cancer in the first 75 years of life.

A Cook

Alastair Cook

And now? This time round the estimated numbers are 128,000 and over 43,000 with one in two men/one in three women discovering they have cancer by time they’re 85. All told, cancer accounts for about three in ten Australian deaths – much the same contribution as heart disease. To add to the gloom the numbers are going up not down so the prediction is 150,000 new cancer cases in 2020.

Not a lot and no surprise

Well, you may be thinking, no change there then – or even I told you so. After all, I’m forever in these pieces elaborating on current cancer stories holding forth about how slow is the progress of science: one step forward, two back, more of a shuffle than a step really, and so on. Or as Martin Schwartz more eloquently puts it, describing science as the art of productive stupidity – being ignorant by choice. This follows almost inevitably from the nature of research because working on what we don’t understand puts us in the awkward position of being ignorant. As Schwartz has it, one of the beautiful things about science is that it allows us to bumble along, getting it wrong time after time, and feel perfectly fine as long as we learn something each time. That’s why I keep telling you to ignore the “great breakthough” newspaper headline dribble – that’s just the hacks trying anything to persuade their editors to give them space to promote themselves.

But wait a mo.

All that sounds consistent with the signs that things in Oz have been going backwards at a rate of knots over the last 20-odd years. But hang on. As ever, bare stats can be a bit misleading (remember what Disraeli said). Thus although around 19,000 more people die each year from cancer than 30 years ago, this is due mainly to population growth and aging – Australian life expectancy has gone up by over four years since 1990 (it’s now 82). The death rate from cancers has fallen by more than 16% and the survival rate for many common cancers has increased by 30 per cent in the past two decades. So that’s great: terrific ad for living in Oz and something of a triumph for medical science.

A sunny side in Oz?

What’s more you can put a positive twist on even the gloomy side of the picture by noting that, if indeed there’s strength in unity, Australia’s trends are much the same as everyone else’s in what we like to call the developed world. Well sort of but there’s a serious negative for Australia Fair, as you might put it, something that sticks out like a sore thumb (or an itchy mole) when you glance at the stats. Between 1980 and 2010 the incidence of skin cancer has shot up in Australia by around 60%. The most common type is non-melanoma skin cancer – usually treatable as it generally doesn’t spread around the body. The nasty version is malignant melanoma – which does metastasize, although is essentially curable if caught before some of its cells escape from the primary site. And the really bad news is that it is now the third most common cancer in Australians and in those aged 15-44 years it is the most common cancer. In 2012, over 12,000 Australians were diagnosed with melanoma and it killed over 1,600. This disease is usually set off by ultraviolet light from sunlight (or sunbeds) damaging DNA (i.e. causing mutations) and you will not have missed the allusion to the fact that people with fair skin (or blue or green eyes/red or blond hair) are most at risk.So the current Oz figures are a bit of a blow to Richie Benaud’s campaign of which I made great play in Slip-Slop-Slap Is Not Enough.

220px-Melanoma_vs_normal_mole_ABCD_rule_NCI_Visuals_Online

ABCD rule illustration: On the left side from top to bottom: melanomas showing asymmetry, a border that is uneven, ragged, or notched, coloring of different shades of brown, black, or tan and diameter that had changed in size. The normal moles on the right side do not have abnormal characteristics (no asymmetry, even border, even color, no change in diameter).

Meanwhile in the lab?

It’s pretty sobering for me to reflect that it was only a few years before I went to Oz that the first human cancer gene (oncogene) was discovered. That was RAS, detected in human cancer cells in 1982 by Geoffrey Cooper at Harvard, Mariano Barbacid and Stuart Aaronson at the NIH, Robert Weinberg at MIT and Michael Wigler at Cold Spring Harbor Laboratory. Between then and 2003 several hundred more cancer genes were identified in a huge frenzy of molecular stamp collecting. Then came the human genome sequencing project and in its wake analysis of tumours on a scale and level of detail that is almost stupefying and would have been unimaginable before 2003. To appreciate the mountain of cancer data that has been assembled over that period, screen the literature data base for research papers that have ‘RAS’ in the title: that is, contain significant info relating to that gene. Answer: 76,000. That’s seventy-six thousand separate pieces of research that have made it through all the peer review and editorial machinery to see the light of day in print. And RAS, massive player though it is, is not the biggest. Do the same check for a gene called P53 and the number is: over 145,000!!

Confused? The plot so far …

First up we noted that the cancer burden in Oz has got a lot heavier over the last 25 years, then we reminded you that advances in science are of the snail-like variety – so you shouldn’t be surprised when things seem to go backwards. But, flipping to the other hand, we trotted out another set of figures saying things have actually got much better (life expectancy and cancer survival rates have steadily climbed). Though, switching hands again, melanoma’s gone through the roof. However, going back to the first hand, if we can still locate it, we noted the massive explosion in the facts mountain of cancer biology for which the blue touch paper was only lit about 25 years ago.

And your parliamentary candidate is …

What with all this sleight-of-hand, flip-flopping and U-turning, it occurs to me that I’m shaping up rather well as a prospective politician. I’m quite taken with the idea, especially as if I stood as an MP in my own constituency I’d be up against Andrew Lansley who, as you’ve probably forgotten, was once upon a time Secretary of State for Health. Being a virtuous and helpful soul, when Betrayed by Nature came out I sent him a copy as a gift, a freebie, – figuring that, as a career civil servant and politician who’d become responsible for the nation’s health, he might find it useful to read a basic primer on something that was killing 150,000 UK citizens every year. Thoughtful, you’d say? Indeed. Did I expect to find him on my doorstep next day gushing gratitude and thirsting for more knowledge? Maybe not, even though he only lives round the corner and we have actually met in the dim past. But at least one might have received a note – a one line email, perhaps – from his PA, who can scarcely be too busy to be polite. But no. Nothing. Zippo. So I came up with a brief sentence that summarised my take on this example of voter wooing, or indeed plain good manners, but I can’t remember it now – for the best perhaps. What is it the Bible says about getting narked? Something along the lines of “whoever says, ‘You fool!’ shall be liable to the hell of fire.”

So thank heavens we’ve side-stepped that but nevertheless, Andrew, it really would be a joy to give you a bloody nose – electorally speaking, of course – so let’s just give those credentials one more buffing. We started by lowering your expectations of science with the reminder that things proceed at a snail’s pace {you do realise that common analogy is very unfair on snails? Scientists have shown they can bowl along at a metre an hour (yippee, we do discover things!) – not much slower than your average supermarket trolley-pusher, but here’s the thing. Snail’s pace means they can get round the garden in one night. That’s the whole of their world covered in one go – without mechanical assistance!! Not so slow after all, eh?}. But the flip side is that the genomic era has already seen the development of a number of drugs that are effective against malignant melanoma. They’re not perfect but at least they take us a step further in dealing with this cancer once it has spread around the body.

And the message?

(That’s quite enough politics, Ed). OK. Let’s abandon a promising career and go back to being a scientist with a typically punchy summary. Australia’s wonderful but when it comes to cancer it’s not much different to any other rich country (not really a flip that, just a statement of fact). Folk are living longer so, of course, more of us will ‘get’ cancer but we seem to think that longevity buys us more time to smoke, booze, burn ourselves pink and eat crappy food. Medical science is doing wonders in detection and treatment: at nearly $400 million a year on cancer research, almost a quarter of all health research expenditure in Australia, it jolly well should. But if we don’t do more to help ourselves the cancer burden is going to overwhelm health resources not just ‘down under’ but all over.

Reference

Schwartz, M.A. (2008). The importance of stupidity in scientific research. J Cell Sci 2008 121:1771; doi:10.1242/jcs.033340

 

Fancy that?

Seeing as they started 28 years ago we can hardly blame members of the Harvard School of Public Health for publishing the results of their labours in tracking 120,000 people, asking them every few years what they’ve eaten and seeing what happened to them (a ‘prospective’ study). About one in five of the subjects died while this was going on but the message to emerge was that eating red meat contributes to cardiovascular disease, cancer and diabetes. The diabetes is non-insulin-dependent diabetes mellitus (NIDDM) or adult-onset diabetes – about 90% of diabetes cases. The cancers weren’t specified, although the evidence for a dietary link is generally strongest for colon carcinoma. The risk is a little higher for processed red meat than unprocessed.

How much?

Massive, if you mean the amount of data they accumulated from such a huge sample size followed over many years. If you mean on a plate, their standard serving size was 85 grams (3 ounces) for unprocessed beef, pork or lamb) and 2 slices of bacon or a hot dog for processed red meat. One of those a day and your risk of dying from heart disease is increased by about 20 per cent and from cancer by about 10 per cent – and the risks are similar for men and women. Just to be clear, that is a daily consumption – and the authors very honestly acknowledge that ‘measurement errors inherent in dietary assessments were inevitable’. They also mentioned that one or two things other than steak can contribute to our demise.

Are we any wiser?

If you recall from Rasher Than I Thought? the risk of pancreatic cancer is increased by just under 20 per cent if you eat 50 grams of processed meat every day. This report suggests that a limit of 1.5 ounces (42 grams) a day of red meat (one large steak a week) could prevent around one in 10 early deaths. So does it tell us anything new? Not really. Was it worth doing? Yes, because it adds more solid data to that summarized in Are You Ready To Order?

And the message?

Unchanged. Do some exercise and eat a balanced diet – just in case you’ve forgotten, that means limit the amount of red meat (try fish, poultry, etc.), stick with the ‘good carbs’ (vegetables, fruits, whole grains, etc.), cut out the ‘bad’ (sugar – see Biting the Bitter Bullet), eat fishy fats not sat. fats and, to end on a technical note, don’t pig out.

 References

Pan A, Sun Q, Bernstein AM; et al. Red meat consumption and mortality: results from 2 prospective cohort studies [published online March 12, 2012]. Arch Intern Med. doi:10.1001/archinternmed.2011.2287.

Pan A, Sun Q, Bernstein AM; et al. Red meat consumption and risk of type 2 diabetes: 3 cohorts of US adults and an updated meta-analysis. Am J Clin Nutr. 2011;94(4):1088-1096.

Rasher Than I Thought?

A recent report concluding that if you eat processed meat (bacon, sausages and suchlike) you’re more likely to get cancer in your pancreas has attracted predictably wide media coverage. More surprisingly, the reports I noticed (BBC News, Sky News and Guardian) were fairly reasonable accounts, quoting the main figures, the source of the information (British Journal of Cancer) and one or two ‘expert’ comments thereon. Usually science reporting in the ‘media’ is more feel than fact and appears to be motivated by coming up with eye-catching headlines rather than precise explanations (being precise, there is a Bacon Eaters Warned Of Deadly Cancer Risk in the above – but let’s not be too critical).

What the papers didn’t say

What such reports almost always fail to mention – and these were no exception – is how devilishly difficult it is to do surveys linking what we eat to what happens to our bodies. One method is to get a group of people with a given disease and ask them what they’ve eaten over the last umpty months/years/decades. You don’t need to be a stats wizard to see the major problem with this! Alternatively, so-called ‘prospective studies’ start with healthy individuals who are followed for exposure to potential factors and subsequent development of disease. Exposed and unexposed sub-groups are compared for disease rates. There are huge problems with these studies too, not the least being that you have no real idea how well the punters stick to the rules – in this case, what they eat.

The predictable upshot over many years has been that, apart from fruit and veg (good anti-cancer stuff, as we all know), for pretty well every survey showing something we eat gives us cancer there’s another that says it either has no effect or it’s actually protective.

Much easier than actually doing either type of survey is to do what these processed meaters did: put together all the sensible studies you can find (in this case eleven prospective surveys between 1966 and 2011) and see if a clear message emerges. Though not perhaps evident at first sight, this is actually quite a useful thing to do because by lumping all the data together you get a large number of patients and controls and the hope is that, out of the confusion of multiple smaller surveys, clarity will come forth.

And, up to a point, it did. The relative risk of pancreatic cancer emerged as 1.19 if you eat 50 g of processed meat every day (it would be 1.00 if you take The World Cancer Research Fund’s advice and avoid the stuff altogether). And, of course, the risk goes up the more of it you eat.

How scary is that?

So where does that leave us and how scared should we be by the scary headline? Have I been unwittingly irresponsible indulging a life-long taste for bacon, sausages and such like? Mmm…bacon…Mmm…sausages. (Sorry – Homeric moment there). Well, something like a 20% risk increase may be significant but it isn’t huge. Then 50 g is a fair wodge of bacon or whatever to eat every day. What’s more, the authors admitted that they’d had to make a few assumptions about just how much processed meat people actually had eaten in the various studies they collated, because some only listed ‘servings’ or ‘times’. Then there’s the question of how is the deed done if processed meat does drive cancer? The study authors noted that the most likely culprit is preservatives commonly added to such food – because these can indirectly cause DNA mutations. Having just salivated round the wondrous display of meats, hams, bacons, sausages etc. in my local Farm Shop (Gog Magog Hills: don’t miss it if you’re anywhere near Cambridge) I note than none of their stuff contains additives or preservatives. Whew!!

And the bottom line…

So my advice to me is: don’t panic, don’t pig out – but do keep an eye on where piggy bits come from. All of which is not to minimise the threat of pancreatic cancer. It’s the eighth biggest cancer killer worldwide, nearly 8,000 Brits died from it in 2008 and there’s no effective treatment. What’s the best thing to do – or not to do? Well, as we’ve said, take it easy on the bacon butties. But two things are strongly associated with pancreatic cancer: smoking (contributes to 20% of cases) and obesity. Not smoking’s easy, of course. Now, how to avoid getting fat…

Reference

Larsson, S.C. and Wolk, A. (2012). Red and processed meat consumption and risk of pancreatic cancer: meta-analysis of prospective studies. British Journal of Cancer advance online publication 12 January 2012; doi: 10.1038/bjc.2011.585.

Sitting on a problem

Spouses around the world whose hubbies spend all their time with their butts parked on the sofa watching wretched football on the t.v. might try informing them that they are significantly increasing their risk of prostate cancer. Breast, lung and bowel cancers get much media coverage, rightly so as the three biggest cancer killers in the western world. But prostate is not far behind (it’s too serious for jokes) – it’s the fifth most common cancer overall – and world-wide it kills 258,000 men a year. Prostate cancer can be treated by surgery, radiation therapy or drugs, including ‘chemical castration’, a phrase guaranteed to send a frisson through any male – though it simply means administering oestrogen to oppose testosterone production. This is effective in many cases but advanced forms of the disease are resistant to chemotherapy and for these there is no real treatment. Thus the news that a new drug, (abiraterone, trade name Zytiga), will come into use next year has to be hailed as a step forward. Abiraterone has just negotiated a phase 3 clinical trial in which (administered with prednisone, the pro-drug of prednisolone) it extended the average survival time for men with advanced prostate cancer from 11 to 15 months and it was approved by the U.S. Food and Drug Administration in April 2011.

Four months doesn’t sound a lot but it is a 36% increase. What’s more, abiraterone works in a different way to chemical castration: instead of stopping testosterone activating its target cells it prevents its synthesis altogether by blocking the action of an enzyme. So this is a totally new targeting strategy.

It isn’t a cure for prostate cancer, so ladies you can still use the stats to get him to do the washing up rather than watching the degrading pantomine that is professional football. But it is a small step in the cancer war and may be the precursor to affecting a major cut in the number of men who die every day from prostate cancer in the UK (28) and in the 28,600 that it kills every year in the USA.

Surviving cancer in the UK and other places

Over the years a number of surveys have concluded that, despite progressive improvements, the UK five-year survival rates for common cancers are worse than the European average by 5 to 15%. The most recent of these has just emerged, comparing survival from four of the most important cancers – breast, bowel, lung and ovarian – at one and five years following diagnosis between 1995 and 2007 in the UK, Denmark, Norway, Sweden, Australia and Canada. Their conclusion was that, despite improvements in survival rates, the disparities remain and that the life expectancy of cancer patients in the UK is shorter than in other countries.

Before we get too downcast by these facts we should note that the UK five-year survival rate for breast cancer, for example, has now reached 82% whereas 40 years ago it was 40%. However, the UK clearly has a problem for which there might be three broad causes: (1) later diagnosis, (2) more aggressive forms of the disease, (3) variable standard of treatment.  It seems probable that all three play a part.

Where you live in the UK bears significantly on your cancer risk.  The National Cancer Intelligence Centre has produced a Cancer Atlas that compares incidence and death rate from the 21 most common cancers in different counties of the UK.  The differences reflect levels of smoking, drinking, poor diet and social deprivation and show that regions of northern England and Scotland are cancer ‘hot spots’.  Their estimate is that if the worst areas could be converted to the best there would be 25,000 fewer new cases and 17,000 fewer deaths a year: with about 156,000 cancer deaths per year that would represent an 11% decrease.

One sensible plan might be to concentrate cancer care into a smaller number of centres of expertise, along the lines of what has been proposed for heart disease.

World, USA and UK cancer deaths 2008.

Reference

Coleman, M.P., Forman, D., Bryant, H., Butler, J., Rachet, B., Maringe, C., Nur, U., Tracey, E., Coory, M., Hatcher, J., McGahan, C.E., Turner, D., Marrett, L., Gjerstorff, M.L., Johannesen, T.B., Adolfsson, J., Lambe, M., Lawrence, G., Meechan, D., Morris, E.J., Middleton, R., Steward, J., Richards, M.A. and the ICBP Module 1 Working Group. (2011). Cancer survival in Australia, Canada, Denmark, Norway, Sweden, and the UK, 1995—2007 (the International Cancer Benchmarking Partnership): an analysis of population-based cancer registry data. The Lancet, 377, 127–138.