Etiology and Pathogenesis
Because of the marked geographical differences in the incidence of gastric carcinoma cited above, together with the change in incidence in migrant populations, it is assumed that there are important environmental factors in the etiology of this disease, but none has been clearly demonstrated. Some association patterns can be described however . Gastric cancer is more common in men than women, blacks than whites, those with a positive familv history, those with blood group A, and those of a lower socioeconomic status. Diet is thought to be an important determinant of risk, possibly relating to high nitrate and salt content. Nitrates can be reduced to nitrites by bacterial action (perhaps more readily in achlorhydric stomachs, since more bacteria are present), which in turn can react with a number of amines to form nitroso compounds. The latter have been demonstrated to be gastric carcinogens in animals. Gastric cancer seems to have a positive association with a diet high in salted fish and meat and pickled vegetables and a negative association with ascorbic acid and fresh vegetables. It is increased in patients with atrophic gastritis (with or without pernicious anemia) and with large (>2 cm) gastric polyps, and after partial gastrectomy for peptic ulcer disease. None of these factors can be clearly related to the decreasing incidence of gastric cancer in the United States cited above.