Newly published research led by the Vanderbilt-Ingram Cancer Center marks a major leap forward in our understanding of breast cancer risk for black women. The largest genome-wide association study among women of African ancestry for breast cancer, researchers investigated upwards of 40,000 genomes looking for variants that may help indicate risk factors for particularly aggressive forms of breast cancer.
The Data on Breast Cancer Risk for Black Women
Breast cancer impacts one in eight women. While death rates have dropped drastically since the ’80s, improvements in outcomes aren’t necessarily equal across all groups of women.
“Black women tend to develop breast cancer at a younger age than White women,” the study explains. “Black women are also more likely than Whites to die from the disease, and they are twice as likely to develop an aggressive subtype called triple-negative breast cancer.“
According to the American Cancer Society, “Black women are still more likely to die from breast cancer than White women across the US, even though Black women have lower breast cancer incidence rates.”
Up until now, this disparity in health outcomes wasn’t well understood, or even studied.
“Before we started this study in 2016, there were just several thousand cases for Black Americans. It was a very small number,” said Wei Zheng,MD PhD, MPH the study’s senior investigator and a cancer epidemiologist at Vanderbilt University.
Studying 40,000 Genomes
Comparing over 20,000 healthy controls to over 18,000 cases of breast cancer in women of African ancestry, the team of researches found genetic variations associated with breast cancer. Focusing on black women in the U.S., Africa and Barbados, the data was collected by the NIH-funded African Ancestry Breast Cancer Genetic consortium, which combined data from 26 studies.
“We have worked with researchers from more than 15 institutions in the [United States] and Africa to establish this large genetic consortium. Data put together in this consortium have been and will continue to be used by researchers around the world to address significant questions related to breast cancer etiology and genetics,” concluded Dr. Zheng.
Estrogen-Negative and Triple-Negative Breast Cancer
“Some breast cancers need your body’s natural hormones—estrogen and progesterone—to grow,” explains the Susan G. Komen Foundation.
“Around 80 out of every 100 breast cancers (around 80%) are oestrogen receptor positive,” notes Cancer Research UK. “Triple negative breast cancers don’t have estrogen, progesterone or HER2 receptors. Around 15 out of 100 breast cancers (around 15%) are triple negative breast cancer. It is more common in younger women.”
Triple-negative breast cancers, along with being more common in younger women, is found most often in women of West African ancestry. This type of breast cancer is also considered more aggressive, growing and spreading faster than other types of cancer.
“Because the cancer cells don’t have hormone receptors, hormone therapy is not helpful in treating these cancers,” explains the American Cancer Society. “And because they don’t have too much HER2, drugs that target HER2 aren’t helpful, either. Chemotherapy can still be useful.”
Clarity on Potential Risk Factors
The research team found 12 locations on the genome that showed significant association with breast cancer. Of those 12, three were found to increase the risk of triple-negative breast cancer.
“Finally, we have enough data to drill down to estrogen negative and triple negative breast cancer, which are twice as common in the African American population as any other population, said Julie Palmer, an author of the study and a cancer researcher at Boston University.
These findings may also help improve modeled risk prediction outcomes, which have historically been calibrated to European risk factors.
