Increased risk of second cancers following breast cancer: Role of the initial treatment

Objectives and methods. The risk of second primary malignancies (SMN) was s tudied in a cohort of 4,416 one-year survivors of a breast cancer. The role of the menopausal status and of the initial treatment modalities (surgery, radiotherapy, and chemotherapy) was investigated. Results. Excluding second primary breast cancer and non-melanoma skin cance r, a total of 193 (4.4%) patients developed a SMN between 1973 and 1992, co mpared with 136 expected (Standardised Incidence Ratio, SIR = 1.4, 95% CI ( 1.2-1.6)). No trend towards either an increase or a decrease was noted in t he SIR with time after treatment (p = 0.2). The greatest increase in the re lative risk concerned soft tissue cancers (SIR = 13.0, 95% CI: 6.8-22.3), f ollowed by leukaemia (SIR = 3.1, 95% CI: 1.7-5.0), melanoma (SIR = 2.7, 95% CI: 1.4-4.8), kidney (SIR = 2.5, 95% CI: 1.2-4.5), ovary (SIR = 2.0, 95% C I: 1.2-3.1) and uterine tumours (SIR = 1.9, 95% CI: 1.4-2.5). The SIR was 3 .0 (95% CI 1.8-4.7) in women under 40 at the time of the breast cancer, 1.9 (95% CI : 1.4 - 2.4) in those aged 40-49 and 1.2 (95% CI 1.0-1.4) in those aged 50 or more. In the 2,514 women who had received radiotherapy as initi al treatment without chemotherapy, the SIR for all SMN was 1.6 (95% CI: 1.1 -2.3) fold higher than in those who had not received radiotherapy as initia l treatment. Conclusion. In conclusion, this study confirms the increased risk of second malignancies in women treated for a breast cancer, and particularly in tho se who were younger at the time of treatment for breast cancer. Our results also suggest that radiotherapy may play a role in the onset of these secon d lesions.