Background: The diagnosis of ductal carcinoma in situ (DCIS) has become increasingly common, but it is not clear which factors predict the development of subsequent breast cancers in these women. The risk of second primary breast tumors was examined in a large, ethnically diverse population-based cohort of women with DCIS. METHODS; California Cancer Registry data on 23,547 women with first DCIS diagnosed in 1988-1999 were examined to estimate the incidence of second DCIS and invasive breast cancer relative to women in the general population. Relative risks were calculated using Poisson regression to estimate which women with DCIS were likely to develop a second DCIS or invasive breast cancer.
Results: Compared to the general population, women with DCIS had significantly increased risk of contralateral DCIS (standardized incidence ratio [SIR] 4.2, 95% confidence interval [CI] 3.7-4.7), contralateral invasive cancer (SIR 1.4, 95% CI 1.2-1.5), ipsilateral DCIS (SIR 4.2, 95% CI 3.5-5.0), and ipsilateral invasive cancer (SIR 1.7, 95% CI 1.4-2.1). Variation by race/ethnicity, age, time, and tumor and treatment characteristics were observed. Black women were 1.9-fold more likely to develop ipsilateral invasive cancer than white women. Young age at onset, comedo histology and having received partial mastectomy only or having neither surgical nor radiation treatment for first DCIS were predictive of ipsilateral cancers.
Conclusions: Close follow-up of women with DCIS is warranted, particularly those who are Black or diagnosed at young age. Investigations should continue to clarify the underlying mechanisms of racial, age, and other differences in second cancer risk.