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Triple-negative breast cancer rates vary by birthplace among black women in US
Prevalence of triple-negative breast cancer among black women in the United States differed considerably by birthplace, according to study results published in Cancer.
In particular, the prevalence rate ratio of this particularly aggressive form of breast cancer appeared 46% lower among black women born in Eastern Africa compared with those born in the United States, according to the researchers.
“The knowledge we have on racial/ethnic heterogeneity of breast cancer is based on a broad categorization, such as black women versus white women. For example, it is well known that black women compared with white women are about two-fold higher risk for developing triple-negative breast cancer,” Hyuna Sung, PhD, principal scientist of surveillance research at American Cancer Society, said in an interview with HemOnc Today.. ” Our result suggests that typical notion of higher proportional burden of triple-negative breast cancer among black women is not generalizable to all women of African descent and simple categorization of breast cancer based on race may mask the complexity of breast cancer heterogeneity that appeared to be present within black women”
The diverse black populations in the United States comprise people born in the U.S. as well as immigrants from various countries. In 2013, about 9% of the black population was born outside the United States, with approximately 50% born in the Caribbean, 35% born in Sub-Saharan Africa, and 9% born in Central and South America.
Sung and colleagues reviewed the National Program of Cancer Registries and U.S. Cancer Statistics to identify 65,211 non-Hispanic black women diagnosed with invasive breast cancer between 2010 and 2015. Recorded birthplaces included the United States (n = 59,380), East Africa (n = 484), West Africa (n = 811) and the Caribbean (n = 4,536).
The researchers compared the rates of triple-negative and hormone receptor-negative breast cancer (negative for estrogen receptor and progesterone receptor) among each foreign-born group of black women with those of U.S.-born black women. They estimated prevalence rate ratios with adjustment for sociodemographic factors and tumor characteristics, stratified analyses by census region and summarized region-specific estimates using random effects meta-analyses.
Compared with U.S.-born black women, prevalence rate ratios of triple-negative breast cancer were as follows: Western-African-born women, 0.92 (95% CI, 0.81-1.04); Caribbean-born women, 0.87 (95% CI, 0.78-0.98); and Eastern-African-born women, 0.53 (95% CI, 0.37-0.77). Thus, the prevalence of triple-negative breast cancer was 13% lower among Caribbean-born women, and 46% lower among Eastern-African-born black women compared with those in the U.S. The 8% lower prevalence among Western-African-born women did not reach statistical significance.
Researchers observed similar patterns for hormone receptor-negative tumors, although the differences between the populations were not as stark. There were no significant differences based on census region (P > .05 for heterogeneity for all).
Nativity (US-born vs. foreign born) has historically served as a surrogate for environmental (vs. genetic) risk factors in epidemiologic studies, Sung told HemOnc Today. Time since immigration is frequently considered together as a proxy of acculturation to a new environment, she added.
“Nationality, or birthplace, among foreign-born population adds another layer, and can serve as a proxy of sociocultural and economic conditions in a broad context,” Sung said. “I suspect there is a variation in well-known breast cancer risk factors such as reproductive and hormonal factors, exogenous hormone use, and lifestyle factors by birthplace among black women, which may have been reflected in the observed difference in subtype distribution among black women.” – by Jennifer Byrne
Disclosures: Sung reports employment with American Cancer Society. Please see the study for all other authors’ relevant financial disclosures.
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Sung H, et al. Cancer. 2019;doi:10.1002/cncr.32293.