(ChemotherapyAdvisor) – Breast cancer estrogen receptor status varies among African-American women depending on region of birth, according to a new study by the American Cancer Society, published in Breast Cancer Research and Treatment.

“Our findings highlight the heterogeneity of breast cancer among black women in the US, which should be considered in future studies of hormone receptor status in these women,” reported Ahmedin Jemal, PhD, and Stacey A. Fedewa, MPH, of the American Cancer Society in Atlanta, Georgia.

Previous studies had found a higher prevalence of ER-negative breast cancers among African-Americans than Caucasians, but those studies did not include information about place of birth, the authors noted.

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The new study included data from 17 Surveillance Epidemiology and End Results (SEER) cancer registries, including African-American patients born in Western Africa (mostly Nigeria), Eastern Africa (mostly Ethiopia), Jamaica, and the US, as well as US-born Caucasian patients. ER-negative tumors were 10% more prevalent among Western African-born women (32.9%) than Eastern African-born women (22%; P<0.001). 

Women born in Africa tended to be diagnosed with breast cancer at a younger age than US-born women, the authors reported; mean age at diagnosis was age 48 years among women born in Africa and 59.1 years among those born in the USA.

Overall, after adjusting for age at diagnosis and other covariates of receptor status, US-born, Western Africa-born, and Jamaica-born African-American women had similar prevalences of ER-negative breast cancer (prevalence ratio [PRR]=0.88, 95% CI, 0.74-1.03), while East-African women had significantly lower prevalence (PRR=0.58; CI, 0.44-0.75). Prevalence of ER-negative tumors decreased with age except among women born in West Africa, for whom prevalence increased with age.

“Notably, the ER-negative prevalence in Eastern-African-born (African-Americans) was comparable to the US-born whites with breast cancer,” Dr. Jemal and Ms. Fedewa wrote.

The reasons for the difference in prevalences among African-American women born in different parts of the world are not yet clear, the authors noted. Common ancestry among African-Americans born in Jamaica, Western Africa, and the US may explain the similarities seen among these women, they suggested; African-Americans brought to the Americas during the trans-Atlantic slave trade came primarily from populations in Western Africa.