Once upon a time (1903 to be exact) a very rich Adelaide family acquired a new member in the form of a little boy whom they christened Norman. Most of the family were doctors and, so well-heeled were they, when young Norm reached the age of 10 they clubbed together and sent him off to the Old Country – and not just to any bit of Merrie England but to Eton (the school, of course, not the rustic parish, generally held to be the most expensive of all – fees currently about £36,000 a year, not counting extras). Norm never returned: South Australia’s loss was Britain’s gain.
We all know what happens to kids that go to Eton – but our Adelaide man was different. For one thing he was very bright and for another he had his family’s love of medicine. He ended up specializing in the thorax – the bit between the neck and the tummy that includes the oesophagus, commonly known as the foodpipe or gullet. Eton probably helped get him started but, even more usefully, some bright spark there gave him the nickname ‘Pasty’ – so great an improvement on Norman that it stuck for life. ‘Pasty’ Barrett ended up as a consultant at St. Thomas’ Hospital where, in 1947, he successfully repaired a ruptured oesophagus – a surgical first for a hitherto fatal condition.
Shortly after that, in 1950, he described finding that sometimes the cells lining the gullet change in appearance, switching from multiple layers of flat cells to a single layer of cells that look like those found in the intestine. We know now that this change is caused by acid from the stomach being squeezed up into the oesophagus. Occasional regurgitation is called heartburn but when it’s persistent it becomes gastric reflux disease – and in about 10% of those cases sustained irritation caused by the stomach juices upsets the cells lining the gullet and they undergo the change to what is now called Barrett’s oesophagus.
Who cares about Barrett’s?
Well, we should all at least take note because a few percent of those with Barrett’s oesophagus will get cancer of the oesophagus, which is now the sixth most common cause of cancer-related death world-wide. Oesophageal cancer has become more common over the last 40 years, men are more prone to it than women and it kills about 15,000 people in the USA each year and nearly 8,000 in the UK. It’s very bad news. Most cases aren’t discovered until the disease has spread and it is then more or less untreatable. The prognosis is dismal: the five-year survival figure is barely 15%. Part of the problem is that the main sign is pain or difficulty in swallowing, often ignored until it is too late.
For many years the only way of finding abnormal tissue was by an endoscopy – a tube with a camera pushed down the throat – both unpleasant and expensive. There has, therefore, been a desperate need for an easy, cheap, non-invasive test to screen for Barrett’s oesophagus.
Enter Rebecca Fitzgerald, a member of the Department of Oncology in Cambridge and a consultant at Addenbrooke’s Hospital, with a brilliantly simple development from earlier attempts to screen the lining of the gullet. The patient swallows a kind of tea-bag on a string which is then pulled up from the stomach. The ‘tea-bag’ is actually a capsule about the size of a multi-vitamin pill containing a sort of honeycomb sponge covered with a coating that dissolves in a few minutes when it reaches the stomach. As the sponge comes up it picks up cells from the gullet lining (about half a million of them) that can then be analysed. The whole gizmo’s called a ‘Cytosponge’. It works with no problems and because it collects cells from the length of the gullet it gives a complete picture, rather than the local regions sampled in biopsies.
What we’ve learned
The hope was that the cells picked up by Cytosponge could be sequenced – i.e. their DNA code could be obtained – and that this would reveal the stages of oesophageal cancer development and hence whether a given case of Barrett’s would or would not progress to cancer. The phases of Barrett’s oesophagus involve a change in the shape of cells lining the tube (from thin, flat cells called squamous epithelial cells to taller columnar cells resembling those in the intestine). This change is called metaplasia: the abnormal cells may then proliferate (dysplasia). If this stage can be detected it’s possible to remove the abnormal tissue by using endoscopic therapy before the condition progresses to full carcinoma.
Remarkably, whole-genome sequences from Barrett’s and from oesophageal carcinoma showed that multiple mutations (changes in DNA sequence) accumulate even in cells that are over-proliferating but look normal. The picture is similar to the ‘battlefield of hundreds of competing mutant clones’ in normal eyelid skin that we saw in The Blink of an Eye.
As the condition progresses the range of mutations increases: in particular, regions of DNA are duplicated – so that the genes therein are present in abnormal numbers. Typically there were 12,000 mutations per person with Barrett’s oesophagus without cancer and 18,000 mutations within the cancer.
Even from this mayhem there emerged mutation patterns (changes in the letters of the DNA code, e.g., A to a G or C to a T) characteristic of the damage caused to the cells lining the oesophagus by splashing stomach acid. These ‘fingerprints’ were found in both Barrett’s and oesophageal cancer – consistent with them being very early events – parallelling the specific mutations in lung cancer caused by tobacco carcinogens.
The great hope was that the spectrum of mutations would identify precursors to cancer and hence those patients requiring treatment. In fact these horribly heterogeneous tissues – a real genetic gemisch – show surprisingly little mutational overlap between Barrett’s oesophagus and oesophageal cancer.
However, it’s possible to take the cells collected by the Cytosponge and screen them for the presence of specific proteins (using antibodies) and it turns out that one in particular, TFF3 (Trefoil Factor 3), provides a highly accurate diagnosis of Barrett’s oesophagus. In addition, although the genetic changes that occur during the progression from Barrett’s to cancer are complex, mutations in one gene (P53 – the ‘guardian of the genome’) are common in pre-cancerous, high grade dysplasia and thus provide an indicator of risk.
All of which means that we haven’t ‘conquered’ oesophageal cancer – but thanks to these remarkable advances we have a much better understanding of its molecular basis. Even more importantly, it’s possible to detect the early stages – and do something about it.
AND … whilst making a major contribution to all this, Rebecca Fitzgerald very kindly found time to make suggestions and provide additional information for this piece.