Subsequent risk of ipsilateral and contralateral invasive breast cancer after treatment for ductal carcinoma in situ: incidence and the effect of radiotherapy in a population-based cohort of 10,090 women

Purpose To assess the effect of different treatment strategies on the risk of subsequent invasive breast cancer (IBC) in women diagnosed with ductal carcinoma in situ (DCIS). Methods Up to 15-year cumulative incidences of ipsilateral IBC (iIBC) and contralateral IBC (cIBC) were assessed among a population-based cohort of 10,090 women treated for DCIS in the Netherlands between 1989 and 2004. Multivariable Cox regression analyses were used to evaluate associations of treatment with iIBC risk. Results Fifteen years after DCIS diagnosis, cumulative incidence of iIBC was 1.9 % after mastectomy, 8.8 % after BCS+RT, and 15.4 % after BCS alone. Patients treated with BCS alone had a higher iIBC risk than those treated with BCS+RT during the first 5 years after treatment. This difference was less pronounced for patients