[Effects of surgery and adjuvant chemotherapy of breast cancer on the incidence of a second malignancy].

Second malignancies were observed in 181 cases after treatment of antecedent breast cancer, among 5,302 primary breast cancer cases. The accumulated incidence of double cancer was as follows: 2.8% for 5 years, 5.2% for 10 years, 7.6% for 15 years, and 10.0% for 20 years. The observed incidence of second malignancy for all sites was 1.58 times as frequent as in the normal group. Statistically significant increased risks were observed for opposite breast cancer (O/E ratio 5.92), ovarian cancer (O/E ratio 4.47), corpus uterine cancer (O/E ratio 5.97) and thyroid cancer (O/E ratio 5.07). Among 5,302 cases, 2,431 (45.9%) underwent adjuvant chemotherapy. In chemotherapy groups, significantly increased risk of stomach cancer, thyroid cancer, leukemia and hepatoma was observed, but there were no remarkable differences between the MMC group and the CPA group. However, in the MMC + CPA combination treatment group, the risk of stomach cancer and leukemia was higher than in the single drug treatment groups. When multiple drugs were administered in large doses as long-term adjuvants, the risk of second malignancy seemed to become greater.