African genetic ancestry may be linked to breast cancer aggressiveness

Key takeaways:

• Higher African ancestry was linked to higher odds of estrogen receptor-negative tumors and triple-negative breast cancer.
• Neighborhood socioeconomic status increases were linked to lower all-cause mortality.

Higher African genetic ancestry was associated with more aggressive tumor subtypes at diagnosis among Black women with breast cancer, according to cohort study findings published in JAMA Network Open.

“While available evidence suggests both genetic and environmental factors may explain excess mortality in Black women, few studies have incorporated them in their design and analysis,” Hari S. Iyer, ScD, MPH, postdoctoral research fellow in Cancer Epidemiology and Health Outcomes at the Rutgers Cancer Institute of New Jersey and the department of medicine at Rutgers Robert Wood Johnson Medical School, and colleagues wrote. “Failure to account for both genetic and neighborhood socioeconomic status factors may lead to overestimates of their relative importance.”

Iyer and colleagues conducted a population-based cohort study with 1,575 women (median age, 55 years) from 10 New Jersey counties who self-identified as Black with histologically confirmed breast cancer from June 2005 to May 2019. All participants were followed until death or censoring in September 2021. Researchers linked a neighborhood socioeconomic status index to residential addresses at breast cancer diagnosis and estimated everyone’s African ancestry percentage.

Overall, median African ancestry was 85% in the cohort. Each 10 percentage point increase in African ancestry was associated with an 8% higher odds of estrogen receptor-negative tumors compared with estrogen receptor-positive tumors (adjusted OR = 1.08; 95% CI, 0.98-1.18). In addition, this 10 percentage point increase in African ancestry was also associated with 14% higher odds of triple-negative breast cancer compared with luminal breast cancer (aOR = 1.15; 95% CI, 1.02-1.31). However, increase in African ancestry was not associated with all-cause mortality or breast cancer-specific mortality.

Overall, 277 all-cause deaths occurred during 11,460 person-years of follow-up.

Higher neighborhood socioeconomic status was associated with lower all-cause mortality (aHR = 0.76; 95% CI, 0.63-0.93) in age-adjusted models. Compared with women in the lowest neighborhood socioeconomic status quartile, those in the highest quartile had a 41% lower rate of all-cause mortality (aHR = 0.59; 95% CI, 0.42-0.83). However, these associations were reduced after further adjusting for potential mediators including individual socioeconomic status, lifestyle factors and comorbidities.

“Screening interventions focused on genetic susceptibility and population-based interventions focused on access, environmental and behavioral factors may help narrow racial disparities in breast cancer,” the researchers wrote.