Heterogeneity of Breast Cancer Clinical Characteristics and Outcome in US Black Women—Effect of Place of Birth

Breast cancer mortality in black women is disproportionately high; reasons for this phenomenon are still unclear. In addition to socioeconomic factors, the biology of the tumor may play a role. We analyzed 1,097 incident invasive breast cancer cases diagnosed between 2000 and 2010 in black US women from Long Island and Brooklyn. Thirty‐five percent of women had an estrogen receptor (ER) negative tumor, 46% a progesterone receptor (PR) negative tumor. ER, PR negative tumors were diagnosed at an earlier age (55.8 versus 55.3 years), at a later stage (p = 0.06), were larger in size (p = 0.04), and more frequently treated with neo‐adjuvant chemotherapy (p = 0.06) than ER, PR positive tumors. Determinants of shorter survival were: ER, PR negativity (HR: 2.2, 95% CI: 1.4–3.4), age, and stage at diagnosis (HR: 2.0; 95% CI: 1.5–2.7). ER, PR negative breast cancer born outside of the US experienced a significantly worse survival than ER, PR negative women who were born in the US. ER, PR negative tumors in black women born outside the US, mainly in the Caribbean, are biologically more aggressive than the same size and age‐matched tumors in black women born in the US. Our study suggests that environmental exposures in the country of origin may impact on host cancer interactions and cancer outcome.