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Researchers have been working for years to determine whether genetic glitches are driving high rates of especially deadly breast cancer in black women in the United States.
Now, the most comprehensive genetic study yet found that one in five black women already diagnosed with breast cancer and referred for genetic counselling had at least one of 18 genetic mutations known to increase the risk of the disease.
The findings, presented at the American Society of Clinical Oncology (ASCO) meeting in Chicago, suggest that inherited mutations may be more common that expected in blacks with breast cancer, pointing to the need for broader genetic counselling and screening among these women and their family members.
Common in black women
Although white women in the United States are slightly more likely to develop breast cancer than black women overall, in women under 45, breast cancer is more common in black women. And it's more deadly.
According to the US Centers for Disease Control and Prevention, black women in the United States have the highest breast cancer death rates of all racial and ethnic groups and are 40% more likely to die of breast cancer than white women.
"For many years, we've seen breast cancer take a heavy toll on African American women, and this study begins to resolve unanswered questions about what's driving these disparities," said Dr Jane Churpek of the University of Chicago.
Churpek and her colleagues used a new genomic test available to academic researchers called BROCA that allowed the team to look at 18 breast cancer susceptibility genes at one time. They tested 249 women with breast cancer who were referred for genetic counselling at the University of Chicago.
Overall, 22% of these women had at least one mutation that increased their risk of breast cancer. Changes in commonly known breast cancer genes BRCA1 and BRCA2 accounted for 79% of the mutations. Women with mutations in these genes have a 37% to 85% lifetime risk of breast cancer, compared with a 12% risk among women in the general population.
"Those are the two that are the best characterised and that we have the best prevention methods for," Churpek said in an interview.
About 21% of the women had mutations in other breast cancer susceptibility genes, including CHEK2, PALB2, ATM and PTEN. The mutations within these genes differed from woman to woman, suggesting the need for more comprehensive testing.
"Almost all of the mutations were different. This is important. For some populations, we can use tests which only look at a few sites in a few genes. That technique will not work in this population with such great genetic diversity," Churpek said.
Deciding when to test
Dr Sylvia Adams, a breast cancer expert at New York University and a spokeswoman for ASCO, said the findings should not be taken to mean that all black women should get genetic testing for breast cancer. Rather, it is a reminder to doctors to refer young black women with breast cancer to a genetic counsellor in the hopes of preventing future cancers among their family members.
"This is to detect an inherited trait that can be passed on to their family members," she said. Adams was not involved in the study.
Churpek also cautioned against using the study findings to draw conclusions about breast cancer risk and the wider community of black women.
Among women included in the study, the main risk factors were the age at which they developed breast cancer and the type, namely triple-negative breast cancer, a very aggressive form of the disease that is especially hard to treat.
Churpek said black women with breast cancer who are young, have triple-negative cancer or have a family member with breast or ovarian cancer should ask their doctors about whether they should get genetic counselling and testing.
Doctors in a press briefing noted that blacks in the United States have been under-studied and that black women with breast cancer are less likely to be referred to genetic counselling services, even among women with a family history of these cancers.
Patients will find other hurdles to comprehensive testing.
The gene test used in the study, BROCA, is available to academic researchers. But doctors practicing outside of academic facilities who want to test for the same genes may have to do so by ordering a series of tests, given that the patents for the BRCA1 and BRCA2 gene tests are held by Myriad Genetics, which prohibits them from being included in broader commercially available tests, Churpek said.
That could change later this month as the US Supreme Court is set to rule on
whether companies can hold patents on human genes.
