There is substantial variation in the prevalence of triple-negative breast cancer among black women by birthplace, affirming that incidence of the disease among black women is not generalizable, according to a new study published in Cancer.
 
Triple-negative breast cancer that is negative for estrogen receptor, progesterone receptor, and human epidermal growth factor 2 receptor, is approximately twice as common among black women than white women in the United States. However, black populations in the United States are diverse and incidence rates may differ by birthplace, the researchers noted.
 
For the study, the authors examined the prevalence of triple-negative and hormone receptor-negative breast cancer among black women in the National Program of Cancer Registries and US Cancer Statistics. Overall, the authors identified 65,211 non-Hispanic black women who were diagnosed with invasive breast cancer from 2010 to 2015. Varying birthplaces in the United States, East Africa, West Africa, or the Caribbean were reported.
 
Compared with US-born black women, the prevalence rate ratio of triple-negative breast cancer was 8% lower among Western-African-born women, 13% lower among Caribbean-born women, and 46% lower among Eastern-African-born black women, according to the study.
 
Examining nativity-related differences among black women can help foster a better understanding of the etiologic heterogeneity of breast cancer, the researchers noted.
 
“It is not clear what risk factors conferred by birthplace are associated with subtype prevalence,” lead study author Hyuna Sun, PhD, of the American Cancer Society, said in a press release. “However, the similarity in breast cancer subtype prevalence between US-born and Western-African-born blacks, contrasted against the differences with Eastern-African-born blacks, may in part reflect shared ancestry-related risk factors.”
 
Despite a previous understanding of the higher proportional burden of breast cancer among black women, the researchers suggested that this notion is not reflective of the diverse black population. Furthermore, a more complete collection of birthplace information in cancer registries can help improve the specificity of understanding potential ancestry-related risk factors.
 
“These findings underscore the importance of considering geographic origin in studies characterizing breast cancer among women of African descent in the United States and elsewhere,” the researchers concluded in the study.
 
References
 
Sung H, DeSantis CE, Fedewa SA, et al. Breast cancer subtypes among Eastern-African-born black women and other black women in the United States. Cancer. 2019. Doi: https://doi.org/10.1002/cncr.32293