Gastrointestinal tract cancers – global burden and trends

ABSTRACTS FROM THE XV MEDICAL SYMPOSIUM BY THE YRJÖ JAHNSSON FOUNDATION ABOUT ETIOLOGY AND PREVENTION OF GASTROINTESTINAL TRACT CANCERS, AUGUST 9-11, 2006.

More than ten million new cancer cases occur each year in the world. Colorectal, stomach and oesophageal cancers are the third, fourth and eighth most common cancers with 1.02, 0.93 and 0.47 million new cases in 2002, respectively [1]. Cancer of the small intestine is, to the contrary, relative rare. Stomach and oesophageal cancers are in general a larger problem in the less developed countries whereas colorectal cancer occurs more frequently in the more developed countries.

However even within these groups of countries, large variations exist. For example, stomach cancer is frequent in Eastern Europe but rather rare in Southern Asia. Huge differences in incidence exist also within countries, e.g., in China and Italy.

The incidence of colorectal cancer shows marked variations between countries, up to a factor of ten. It is important with colorectal cancer that the incidence is focused on rather than mortality, particularly when observing developments over time. Mortality rates may suggest that the disease risk would be in a decrease whereas the opposite is most often true.

The standard of living does not directly associate with colorectal cancer risk. For example, in many former socialist countries, colorectal cancer incidence has been higher than in Finland. There has been a striking increase in incidence in Japan where the rates have reached or passed those observed in the USA. Migrant studies show that the migrants’ and their descendants’ incidence rates gradually approach the rates in the new host country.

In stomach cancer, the incidence trends are invariably in a decrease. However, for example in Japan where incidence is high, the decrease has been so far rather modest. The Japanese rates are affected to an extent by a screening program and different diagnostic criteria. Migrant studies show a similar convergence of incidence as observed in colorectal cancer.

Although the overall stomach cancer incidence has been in a decrease, the incidence of cancer in gastric cardia has been reported to increase in the USA and some other Western countries. Possibilities that have been discussed as a background for this increase include increased specificity of location and misclassification with distal oesophageal adenocarcinoma. Swedish Cancer Registry's data from the late 1990s show a marked classification problem but in general it may be concluded that cancer in gastric cardia is epidemiologically a different entity from the rest of stomach cancer.

In oesophageal cancer the international incidence rates vary by a factor 20. Huge variations exist in Africa, Europe and within Iran and China. Time trends are heterogeneous. The rates in migrants approach again those of the host population. The trend heterogeneity may be in part accounted for by the incidence of adenocarcinoma that has experienced an increase, particularly in males in many Western countries. Misclassification is even here a factor to be considered although it is quite evident that the increase cannot be attributed more than to a small extent to this problem.

Gastrointestinal cancers tend to be more common in males than females. The rates are closest between sexes in colon cancer and most different in adenocarcinoma of the oesophagus. The international variations and trends suggest that these cancers are particularly dependent on external factors and may thus be to a large extent preventable by affecting those factors, once they have been identified. This is a good challenge to analytic epidemiology and basic research on cancer.