Stomach Cancer Declining: Related to H. Pylori, Poor Quality Food, Smoking and Alcohol
Thirty-eight percent of cases occur in China The rates are low in Eastern and Northern Africa, North America, and South and Southeast Asia
The differences in risk among countries are related to dietary factors
The importance of Helicobacter pylori has been recognized. H. pylori accepted as a human carcinogen
Stomach cancer is the second most frequent cancer, with 798,000 new cases (9.9% of the total) and 628,000 deaths (12.1% of cancer deaths), although it is only in fourth rank in women (Fig. 2).
Thirty-eight percent of cases occur in China, where it remains the most common cancer in both sexes, as it is elsewhere in Eastern Asia. Age-standardized incidence rates are highest in Japan (77.9 per 100,000 in men, 33.3 per 100,000 in women). High rates are also present in both sexes in Eastern Europe and tropical South America (Fig. 4). The rates are low in Eastern and Northern Africa, North America, and South and Southeast Asia (age-standardized incidence rate in men 5.9 to 9.0 per 100,000 and 2.6 to 5.3 per 100,000 in women).
Survival for stomach cancer is moderately good only in Japan (53%), where mass screening by photofluoroscopy has been practiced since the 1960s. Other areas with better survival are North America (21% based on the SEER data, 34% age-adjusted estimate) and Australia and New Zealand (29%), possibly because of early diagnosis after a greater number of endoscopic examinations performed for gastric disorders. Survival is 18% on average in European registries and is consistent with the age-adjusted estimates. Elsewhere, survival varies from 10% (Eastern Europe, including Russia) to 21% in Latin America.
The differences in risk among countries are usually assumed to be related to dietary factors, which are important in determining the risk of individuals in epidemiologic studies. Their importance is consistent with the descriptive data and studies of migrants.
Recently, the importance of Helicobacter pylori has been recognized. The IARC12 has accepted H. pylori as a human carcinogen, based on ecological correlation studies (such as the EUROGAST study13), a host of case-control studies, and, more usefully, several cohort studies. The combined odds ratio from these studies is 2.1.14H. pylori is assumed to have an indirect action because it provokes gastritis, which is a precursor of gastric atrophy, metaplasia, and dysplasia. The role of dietary and other exogenous factors may be synergistic or antagonistic.
The proportion of the population infected with H. pylori is large in developing countries, ranging from 80% to 90%; individuals contract the infection at a young age, and it persists throughout life. In developed countries, the prevalence is lower. Assuming a value of 50% (and 80% in developing countries) and a relative risk of 2.1, the number of new cases of stomach cancer attributed to the bacterium is 337,800, representing 42% of the world total of these cancers (47% in developing countries and 35% elsewhere).
A steady decline has occurred in gastric cancer incidence and mortality in most countries. Our world estimate of the number of new cases in 1990 was just 6% greater than that in 1985, which, given the population increase and aging, represents a decline of 4% to 5% in age-adjusted risk. This decline may be related to improvements in preservation and storage of foods. It also may represent changes in the prevalence of H. pylori by birth cohort, perhaps because of reduced transmission in childhood, following a trend toward improved hygiene and reduction of crowding.15
In any case, one can confidently expect a continuing decline in age-adjusted incidence and mortality from stomach cancer. If the observed rate of decline in the last 5 years continues, the expected number of new cases in 2010 will be about 1 million, an increase of 30% rather than the 58% additional cases resulting simply from population growth and aging.