Second malignancy in stomach cancer patients and its possible risk factors.

To identify possible risk factors of multiple primary cancers in stomach cancer patients, a case-control analysis based on data from medical records was conducted on 73 patients (54 males and 19 females) with stomach cancer who were affected by one or more other primary cancers subsequently or concurrently (cases) and 146 patients with stomach cancer alone (controls), by matching sex, age, time of the operation for stomach cancer and survival period. The relative risks (RR) for cancer history in the father (RR = 3.21), for family history of stomach cancer (RR = 2.52) and for history of hemorrhoids (RR = 3.15) were significantly increased in both sexes. The proportion of professionals in males was significantly higher in cases than in controls. In a conditional multiple logistic regression analysis for males, the adjusted relative risk (aRR) for family history of cancer in two or more members (aRR = 3.54) was statistically significant. Smoking tended to increase the risk of multiple primary cancers in males, especially in the cases with smoking-related second malignancy (RR = 4.83). These data suggest the possibility that both genetic and environmental factors are involved in the multiplicity of cancer in stomach cancer patients.