Research Article Racial Comparison of Receptor-Defined Breast Cancer in Southern African Women: Subtype Prevalence and Age– Incidence Analysis of Nationwide Cancer Registry Data

Background: Receptor-defined breast cancer proportions vary across Africa. They have important implica-tions for survival prospects and research priorities. Methods:Westudied estrogen receptor (ER), progesterone receptor (PR), andHER2 receptor statuses in two multiracial Southern African countries with routine diagnostic immunohistochemistry. A total of 12,361 women with histologically confirmed breast cancer diagnosed at age 20 years during (i) 2009–2011 from South Africa’s national cancer registry (public sector) and (ii) 2011–2013 from Namibia’s only cancer hospital were included. Crude, age, and ageþ laboratory–adjusted ORs of receptor status were analyzed using logistic regression, and age–incidence curves were analyzed using Poisson regression. Results: A total of 10,047 (81%) women had known ER status. Ranking of subtypes was consistent across races: ERþ/PRþHER2was most common (race-specific percentage range, 54.6%–64.8%), followed by triple-negative (17.4%–21.9%), ERþ/PRþHER2þ (9.6%–13.9%), and ERPRHER2þ (7.8%–10.9%). Percentages in black versus white women were 33.8 % [95 % confidence (CI), 32.5–35.0] versus 26.0 % (24.0–27.9) ER; 20.9% (19.7–22.1) versus 17.5 % (15.4–19.6) triple-negative; and 10.7 % (9.8–11.6) versus 7.8 % (6.3–9.3) ERPRHER2þ. Indian/Asian andmixed-ancestry women had intermediate values. Age–incidence curves had similar shapes across races: rates increased by 12.7 % per year (12.2–13.1) across ER subtypes under the age of 50 years, and thereafter slowed for ERþ (1.95%) and plateaued for ER disease (0.1%). Conclusions: ERþ breast cancer dominates in all Southern African races, but black women have a modest excess of aggressive subtypes. Impact: On the basis of the predominant receptor-defined breast tumors in Southern Africa, improving survival for the growing breast cancer burden should be achievable through earlier diagnosis and appropriate treatment. Cancer Epidemiol Biomarkers Prev; 23(11); 2311–21. 2014 AACR