Ecology of stomach cancer in Chile.

The results of a case-control study and one on nitrate ecology are summarized. Patients attending gastroscopy clinics in 8 participating hospitals in Santiago were interviewed before their diagnoses were known. Of these patients, 360 with stomach cancer were matched to those with noncancerous diseases who were selected from the pool, and we found that 1) patients lived in high-risk areas for longer periods in early life than did controls; 2) controls lived in low-risk areas for longer terms than did the patients; and 3) an association existed between stomach cancer and occupation in agriculture. In a subgroup of 98 patients for whom histologic classification was available, the association with residence in early life in a high-risk area was seen only for patients with intestinal type stomach cancer. Nitrate levels in urine and nitrite levels in saliva were determined in school children 11-13 years of age in 2 areas of high-risk in central Chile and in 2 areas of low risk for stomach cancer located in the extreme northern and southern regions. Levels of both nitrates and nitrites were concurrently determined in selected vegetables. The results are apparently incompatible with the hypothesis of high nitrate intake in areas of high stomach cancer incidence. This paradoxical finding led us to suggest that cofactors are involved in the pathopoiesis of stomach cancer that promote or inhibit the formation of nitrosamines.