While breast cancer is the most common cancer among women in the United States, not all breast cancers are the same. There are different types of breast cancer, which are determined by the specific cells in the breast that are affected, according to the American Cancer Society.
“Triple-negative breast cancer accounts for 15 percent of breast cancer in the Caucasian population and 35 percent in the African-American population," Dr. Fergus Couch, lead author of the study, said in a press release. "It is also associated with an increased recurrence risk and poor five-year survival rates relative to other breast cancers."
A woman faced with breast cancer, of course, hopes for a definitive test that can tell her what form of cancer she has, and the best steps to treat it. Right now, genetic testing for breast cancer looks mostly at the genetic changes that come from a person's parents and grandparents, and the increased risk of being genetically predisposed to some cancers.
But only 5 to 10 percent of breast cancers are inherited genetically, according to the American Cancer Society. Triple-negative breast cancer is one of the hardest types of breast cancer to treat because it moves so quickly that screening tests don’t often “catch it” before it becomes serious.
So, what exactly is triple-negative breast cancer?
This type of cancer means that the three most common genes that indicate breast cancer growth -- estrogen, progesterone, and the “human epidermal growth factor receptor-negative” (HER-2) gene -- aren’t in the cancer tumors. Since these tumor cells don’t have those receptors, common treatments like hormone therapy and the usual drugs that target estrogen, progesterone, and HER-2 may be ineffective.
For the study, Couch and his colleagues performed genetic testing on almost 11,000 women with triple-negative breast cancer. They tested up to 21 cancer genes that make breast cancer more likely. The genes, when altered, that increased the risk of triple-negative breast cancer in the women studied included BARD1, BRCA1, BRCA2, PALB2, and RAD51D. If those genes are involved, there’s a greater than 20 percent lifetime risk for all types of breast cancer among white women. In addition, mutations in the BRIP1 and RAD51C genes were linked to a more moderate risk of triple-negative breast cancer, and a similar trend held true for African Americans.
“This study is the first to establish which genes are associated with high lifetime risks of triple-negative breast cancer,” Couch said.
This study “shows this in more detail, and identifies new specific and strong associations between the susceptibility genes RAD51D and BARD1 and triple-negative breast cancer risk,” he added.
Couch believes these findings might lead to revisions to the National Comprehensive Cancer Network screening guidelines, which currently recommend only BRCA testing when a patient has a family history of breast cancer or is diagnosed at age 60 or younger. Of course, this study must have its results duplicated before doctors are sure of the association, but this may be a win for the possibility that expanded genetic testing may help identify women at risk for triple-negative breast cancer -- and lead to better prevention strategies.
Dr. Ryan Guinness is an internal and preventive medicine resident physician at the University of California, San Francisco, currently working in the ABC News Medical Unit.