Second primary cancers following breast cancer in the Japanese female population.

To assess the risk of developing second primary cancers following breast cancer in Japanese females, we performed a retrospective cohort study of 2786 patients who were newly diagnosed with breast cancer at our hospital between 1970 - 1994, until the end of 1995 (average follow-up period, 8.6 years). The expected number of each second primary cancer was calculated by multiplying the number of appropriate person-years at risk by the corresponding age- and calendar period-specific cancer incidence rates for women obtained from the Osaka Cancer Registry. One hundred and seventeen patients developed a second primary cancer other than subsequent breast cancer, yielding an observed-to-expected ratio (O / E) of 1.3 [95% confidence interval (CI) = 1.1 - 1.6]. The risk for developing a second primary cancer was significantly elevated during the first year following the diagnosis of breast cancer, and decreased with the passage of time to unity. A significantly increased risk was noted for the development of ovarian cancer (O / E = 2.4, 95% CI = 1.0 - 4.6), thyroid cancer (O / E = 3.7, 95% CI = 1.5 - 7.6) and non-Hodgkin's lymphoma (NHL) (O / E = 3.5, 95% CI = 1.4 - 7.1) among the breast cancer patients compared with the general population. Patients who received hormonal therapy as the breast cancer treatment showed a significantly increased risk for ovarian cancer (O / E = 5.5, 95% CI = 1.8 - 12.9). Patients who received chemotherapy as the breast cancer treatment had an increased risk for NHL (O / E = 5.0, 95% CI = 1.6 - 11.6). These findings indicate that Japanese female patients with breast cancer had a 30% higher risk of developing a second primary cancer than the general population, the higher risk being manifested in the early period following the diagnosis of breast cancer. Medical surveillance of breast cancer patients for NHL, as well as for ovarian cancer and thyroid cancer, is required.