Racial comparison of receptor-defined breast cancer in Southern African women: Subtype prevalence and age-incidence analysis of nationwide cancer registry data.

Authors: C Dickens, R Duarte, A Zietsman, Herbert C, P Kellet, J Schuz, D Kielkowski, V.A McCormack

Source: Cancer Epidemiology, Biomarkers And Prevention. OnlineFirst August 20, 2014; Doi: 10.1158/1055-9965. EPI-14-0603

Summary

Background: Receptor-defined breast cancer proportions vary across Africa. They have important implications for survival prospects and research priorities.

Methods: We studied estrogen (ER), progesterone (PR) and human epidermal growth factor-2 (HER2) receptor statuses in two multiracial Southern African countries with routine diagnostic immunohistochemistry. 12361 women with histologically-confirmed breast cancer diagnosed at age ≥20 during (i) 2009-2011 from South Africa’s national cancer registry (public sector) and (ii) 2011-13 from Namibia’s only cancer hospital were included. Crude, age and age+laboratory adjusted odds ratios of receptor status were analyzed using logistic regression and age-incidence curves analyzed using Poisson regression.

Results: 10047 (81%) women had known ER status. Ranking of subtypes was consistent across races: ER⁺/PR⁺HER2^– was most common (race-specific percentage range: 54.6 to 64.8%), followed by triple-negative (17.4 to 21.9%), ER⁺/PR⁺HER2⁺ (9.6 to 13.9%), and ER^–PR^–HER2⁺ (7.8 to 10.9%). Percentages in black vs. white women were 33.8% (95% CI: 32.5 35.0) vs. 26.8% (24.1-29.4) ER^–; 20.8% (19.6-22.0) vs. 16.6% (14.6-18.8) triple-negative; and 10.5% (9.6-11.4) vs. 7.1% (5.7-8.7) ER^–PR^–HER2⁺. Indian/Asian and mixed-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 age 50, and thereafter slowed for ER⁺ (1.95%) and plateaued for ER^– disease (-0.1%).

Conclusions: ER+ breast cancer dominates in all Southern African races, but black women have a modest excess of aggressive subtypes.

Impact: Based on the predominant receptor-defined breast tumors in Southern African, improving survival for the growing breast cancer burden should be achievable through earlier diagnosis and appropriate treatment.