Why Do African Americans Have Worse Breast Cancer Outcomes?

Researchers determine mechanism for poor survival rates in African American patients with estrogen-receptor positive breast cancer.

A strong survival mechanism in cancer cells appears to be partially responsible for poorer outcomes in African American women with estrogen-receptor positive (ER+) breast cancer.

In a study presented at the American Association for Cancer Research annual meeting, researchers report that breast tumors from African American patients have reduced sensitivity to the cancer drug tamoxifen as a result of increased activation of the unfolded protein response (UPR) in cancer cells.

When UPR is activated as a result of stress within cancer cells caused by the treatment, the pro-survival pathway becomes activated to allow tumor cells to survive the therapy.

"From our gene analyses, we found increased activation of the UPR pro-survival pathway in African American patients, compared with other patients, along with increased activity of a number of genes associated with that pathway," study lead investigator Ayesha Shajahan-Haq, PhD, said in a press release. "This can lead to increased resistance to common therapies."

Approximately 70% of all breast cancers are ER+, which means they depend on estrogen to grow. In many cases of ER+ cancers, treatment includes blocking estrogen from reaching cancer cells, but nearly 50% of tumors develop resistance to treatment. In a comparison of African American women with ER+ who are treated similarly to European-American women, African Americans have worse progression-free and overall survival due to undetermined reasons.

"Our findings offer a partial understanding of racial differences within ER+ breast cancers," Shajahan-Haq said. "We demonstrate both increased resistance to anti-cancer therapy in African-American patients as well as the reason that resistance occurs."

Treatment strategies that target the UPR pathway could improve treatment resistance to provide more effective therapy for these patients, the researchers concluded.

"Biology may not be the only factor contributing to the racial disparities in outcome in the general public,” Shajahan-Haq said. “Factors such as access to mammography, follow-up care or treatment, income status and other social factors have also been shown to contribute to disparities in outcome."