Although the odds of developing breast cancer are nearly identical for black and white women, black women are 42 percent more likely to die from the disease. This mortality gap – driven by social and environmental, as well as biological factors – continues to persist.

A large, multi–institutional study, published on–line May 4, 2017, in JAMA Oncology journal, was designed to understand this gap by beginning to unravel the germline genetic variations and tumor biological differences between black and white women with breast cancer. This is the first “ancestry–based comprehensive analysis of multiple platforms of genomic and proteomic data of its kind,” the authors note.

Findings from this study could lead to more personalized risk assessment for women of African heritage and hasten the development of novel approaches designed to diagnose specific subtypes of aggressive breast cancers early and treat them effectively.

One new finding is that black women with hormone receptor positive, HER2–negative breast cancer had a higher risk–of–recurrence score than white women. The study also confirmed that black patients were typically diagnosed at a younger age and were more likely to develop aggressive breast–cancer subtypes, including basal–like or triple–negative cancers (tumors lacking estrogen receptors, progesterone receptors and HER2), as well as other aggressive tumor subtypes.

“People have long associated breast cancer mortality in black women with poverty, or stress, or lack of access to care, but our results show that much of the increased risk for black women can be attributed to tumor biological differences, which are probably genetically determined,” said study author Olufunmilayo Olopade, MD, professor of medicine and human genetics at the University of Chicago.

“The good news,” she said, “is that as we learn more about these genetic variations, we can combine that information with clinical data to stratify risk and better predict recurrences – especially for highly treatable cancers – and develop interventions to improve treatment outcomes.”

The study used DNA data collected from 930 women – 154 of predominantly African ancestry and 776 of European ancestry – available through The Cancer Genome Atlas (TCGA), established by the National Cancer Institute and the National Human Genome Research Institute. The researchers combed through the data methodically, looking for racial differences in germline variations (normal DNA), somatic mutations (tumor acquired), subtypes of breast cancers, survival time, as well as gene expression, protein expression and DNA methylation patterns.

“Most significantly,” explained first author Dezheng Huo, MD, PhD, associate professor of public health sciences at the University of Chicago, “we observed a higher genetic contribution to estrogen–receptor negative breast cancer in blacks.”

The study also revealed 142 genes that showed differences in expression levels according to race. One gene, CRYBB2 (Crystallin Beta B2), was consistently higher in tumors from black patients within each breast cancer subtype, as well as in normal tissues, suggesting it may be a race–specific gene.

The researchers also found somatic mutations in 13 genes or DNA segments that differed in frequency in tumors from black and white women. One of them, a mutated gene called TP53, was more common in black women (52%) than white women (31%) and was a strong predictor of disease recurrence. “This study now outlines a path for us to personalize breast cancer risk assessment and develop better strategies to empower all women, especially black women, to know their genetics and be more proactive in managing their risk,” Perou said.