Familial aggregation of stomach cancer has long been observed. The effect on disease risk of family history and its magnitude according to the type of affected relatives, however, is not well known. We conducted a prospective analysis using the JACC study (Japan Collaborative Cohort Study For Evaluation of Cancer Risk, sponsored by Monbusho) data. During the follow-up period, 662 stomach cancer deaths were documented. A positive history of stomach cancer in one or more first-degree relatives was associated with a significantly increased risk of death from the disease in both men (RR 1.60; 95% CI 1.11-2.31) and women (RR 2.47; 95% CI 1.50-4.06). In the subanalysis stratified by age, the association between positive family history and stomach cancer was stronger in the age group from 40-59 (RR 2.62; 95% CI 1.34-5.11 for men and RR 5.88; 95% CI 2.70-12.82 for women) than in the age group from 60-79 (RR 1.31; 95% CI 0.84-2.05 for men and RR 1.44; 95% CI 0.72-2.88 for women). In the age group from 40-59, men with father's history and women with mother's and sister's history of the disease had a significantly increased risk (RR 3.14; 95% CI 1.51-6.55, RR 10.46; 95% CI 4.54-24.12, RR 13.39; 95% CI 3.89-46.12, respectively). When 2 or more family members were affected, the increment in the risk was prominent especially in women (RR 9.45; 95% CI 4.46-20.05). These results suggest the existence of a certain subtype of stomach cancer that is inherited more often by women from one generation to the next in gender-influenced fashion. Any preventive strategy should take into account the degree of individual susceptibility.
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