Risk factors of multiple primary cancers in breast cancer patients.

To clarify risk factors of multiple primary cancers in breast cancer patients, a case-control analysis based on data from medical records was conducted at the Aichi Cancer Center Hospital. For each of a total of 115 multiple primary cancer patients affected by one or two other primary cancers after or concurrently with breast cancer, two patients with unilateral breast cancer were selected as controls by matching age, time of the operation for breast cancer, and survival period. Multiple primary cancer patients were then divided into two groups, 61 cases of bilateral breast cancer and 56 cases of other multiple primary cancers. Conditional multiple logistic regression analysis indicated that relatively heavy smoking (more than 10 cigarettes per day) decreased the risk of multiple primary cancers taken overall (relative risk (RR) = 0.23); overweight status elevated the risk of bilateral breast cancer (RR = 3.01); and greater than average height (RR = 2.20), history of gallstone or cholecystitis (RR = 6.29), and late first birth or nulliparous status (RR = 6.85) elevated the risk of other multiple primary cancers. The effects of weight and height were predominant in the postmenopausal women. As to family history, we could not obtain clear results, though history of cancer among siblings tended to increase the risk of multiple primary cancers (P less than 0.10) and family history of breast cancer was more frequent in patients with bilateral breast cancer (not significant).