Increased risk of second malignancies after in situ breast carcinoma in a population-based registry.

Among 1276 primary breast carcinoma in situ (BCIS) patients diagnosed in 1972-2002 in the Southern Netherlands, 11% developed a second cancer. Breast carcinoma in situ patients exhibited a two-fold increased risk of second cancer (standardised incidence ratios (SIR): 2.1, 95% confidence interval (CI): 1.7-2.5). The risk was highest for a second breast cancer (SIR: 3.4, 95% CI: 2.6-4.3; AER: 66 patients per 10,000 per year) followed by skin cancer (SIR: 1.7, 95% CI: 1.1-2.6; AER: 17 patients per 10,000 per year). The increased risk of second breast cancer was similar for the ipsilateral (SIR: 1.9, 95% CI: 1.3-2.7) and contralateral (SIR: 2.0, 95% CI: 1.4-2.8) breast. Risk of second cancer was independent of age at diagnosis, type of initial therapy, histologic type of BCIS and period of diagnosis. Standardised incidence ratios of second cancer after BCIS (SIR: 2.3, 95% CI: 1.8-2.8) resembled that after invasive breast cancer (SIR: 2.2, 95% CI: 2.1-2.4). Surveillance should be directed towards second (ipsi- and contra-lateral) breast cancer.