In Reply Denu suggests that biological differences between breast cancers in black and white patients are largely explained by disparities in access to care, in particular disparity in screening.
Our study demonstrated that the proportion of aggressive triple-negative (TNBC) breast cancer was higher in black patients than in white patients, even though the tumor stage was similar between the 2 racial groups in The Cancer Genome Atlas (TCGA).1 While we do not know whether tumors in TCGA were screen-detected cancers, we used ancestry-informative genomic markers to define racial groups. The similarly advanced stage at diagnosis between African ancestry and European ancestry patients suggests that mammography screening status is unlikely to account for the observed racial differences in breast cancer subtypes. Furthermore, our study1 and other publications2 demonstrated higher frequencies of estrogen receptor–negative breast cancer risk alleles in blacks than in whites, thus providing a genetic explanation for the difference in the frequency of TNBC. Moreover, TNBC is more likely to present as interval cancers even among women undergoing regular screening by mammography. Thus, it is unlikely that mammographic screening practices explain changes in tumor characteristics. Instead, lifestyle, environmental, and genetic risk factors probably determine breast cancer characteristics and why women of African ancestry across the Diaspora more often receive a diagnosis of aggressive young-onset TNBC and human epidermal growth factor receptor 2 (ERBB2 [formerly HER2])–enriched breast cancers.3