Malignant breast tumors after radiotherapy for a first cancer during childhood.

Purpose To assess the specific role of treatment and type of first cancer (FC) in the risk of long-term subsequent breast cancer (BC) among childhood cancer survivors. Patients and Methods In a cohort of 1,814 3-year female survivors treated between 1946 and 1986 in eight French and English centers, data on chemotherapy and radiotherapy were collected. Individual estimation of radiation dose to each breast was performed for the 1,258 patients treated by external radiotherapy; mean dose to breast was 5.06 Gy (range, 0.0 to 88.0 Gy) delivered in 20 fractions (mean). Results Mean follow-up was 16 years; 16 patients developed a clinical BC, 13 after radiotherapy. The cumulative incidence of BC was 2.8% (95% CI, 1.0% to 4.5%) 30 years after the FC and 5.1% (95% CI, 2.1% to 8.2%) at the age of 40 years. The annual excess incidence increased as age increased, whereas the standardized incidence ratio decreased. On average, each Gray unit received by any breast increased the excess relative risk of BC by 0.13 (< 0...