23 August 2012

Cause of global throat cancer epidemic a mystery

by Will Parker

The "astounding" increase in cases of esophageal cancer around the world seems to have begun in the UK in the 1950s, but a recent comprehensive analysis of historical data has brought scientists no closer to identifying the cause. The new report into what medicos call a "global epidemic" appears in the journal Gut.

There are two distinct types of gullet (esophageal) cancer - squamous and adenocarcinoma, the latter typically affecting the lower third of the esophagus. It was first observed that diagnoses of adenocarcinoma were increasing rapidly in the mid-1980s, but the reasons behind this dramatic increase are still an enigma.

In a bid to identify any discernible patterns, the authors of the new report looked at data from 16 population based cancer registries in eight countries (Australia, Denmark, England, Finland, Norway, Scotland, Sweden and the US), going back between 29 and 54 years.

The researchers calculated the rates of the disease that would be expected to be diagnosed, according to the age of the population and looked at the timelines to see if there were particular flash points at which diagnoses suddenly increased.

They found that the incidence of esophageal adenocarcinoma continued to increase rapidly in all 16 registries, and there is little evidence that this trend is beginning to plateau. Men continue to be 3-9 times as likely to develop the disease as women - a pattern that has remained consistent over time.

The researchers note that in around half the registers, a low and seemingly stable rate of new diagnoses shifted abruptly to a rapidly and consistently linear increase. In the remainder of the registries, the rate had gone beyond a low and stable phase, and was already rising when registration started.

Timeline analysis indicated that the first discernible surge probably occurred around 1960 in Scotland and England, with a similar surge in the US starting in the mid-1970s, and another beginning in 1991 in Sweden.

The authors suggest that as the analysis was restricted to countries and regions with reliable and longstanding data, it seems unlikely that more than a fraction of these patterns could be attributable to mistakes in diagnosis.

Obesity, which is linked to acid reflux - a well known cause of the disease - has been rising rapidly, but the pattern does not fully match that of esophageal adenocarcinoma, say the authors, nor does it explain the gender difference seen in this type of cancer. Smoking rates do not appear to be linked either, and both factors are "unlikely to explain either the abrupt change or the astounding rate of increase," the authors note.

"Therefore," they conclude, "it seems reasonable to hypothesize that the effects of a strong, highly prevalent and yet unidentified causal factor - first introduced in the UK in the middle of the 20th century - have been superimposed on the effects of known risk factors."

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Source: British Medical Journal