Racial disparities in risk of second breast tumors after ductal carcinoma in situ

The purpose of the study was to examine the impact of race/ethnicity on second breast tumors among women with ductal carcinoma in situ (DCIS). We identified 102,489 women diagnosed with primary DCIS between 1988 and 2009 from the 18 NCI-SEER Registries. Cox proportional hazard regression was used to estimate race/ethnicity-associated relative risks (RRs) and their 95 % confidence intervals (CI) of ipsilateral breast tumors (IBT; defined as DCIS or invasive carcinoma in the ipsilateral breast) and contralateral breast tumors (CBT; defined as DCIS or invasive carcinoma in the contralateral breast). Overall, 2,925 women had IBT and 3,723 had CBT. Compared with white women, black (RR 1.46; 95 % CI 1.29–1.65), and Hispanic (RR 1.18; 95 % CI 1.03–1.36) women had higher IBT risk, which was similar for invasive IBT and ipsilateral DCIS. A significant increase in IBT risk among black women persisted, regardless of age at diagnosis, treatment, tumor grade, tumor size, and histology. The CBT risk was significantly increased among black (RR 1.21; 95 % CI 1.08–1.36) and Asian/PI (RR 1.16; 95 % CI 1.02–1.31) women compared with white women. The association was stronger for invasive CBT among black women and for contralateral DCIS among Asian/PI women (P_{heterogeneity} < 0.0001). The black race-associated CBT risk was more pronounced among women ≥50 years at diagnosis and those with comedo DCIS; in contrast, a significant increase in risk among Asian/PI women was restricted to those <50 years and those with noncomedo DCIS. Racial/ethnic differences in risks of second breast tumors after DCIS could not be explained by pathologic features and treatment.