4/18/2018 7:58:00 AM At-home test for breast cancer mutation not comprehensive
Dear Doctor: I don't have a history of breast cancer in my family, but now that there's an at-home test for the BRCA mutations, should I get tested just in case? It has to be less expensive than going to a doctor, and it might provide some peace of mind.
Dear Reader: Having peace of mind that you don't have a serious disease cannot be understated. For women, knowing that they're at lower risk of developing breast cancer can be especially reassuring.
Now for some background on the genes that the at-home test assesses: BRCA1 and BRCA2. For starters, they're tumor-suppressor genes, producing proteins that aid in the repair of damaged DNA molecules. If the proteins produced by the BRCA genes don't work appropriately, abnormal cells with DNA mutations will not be repaired but will instead divide to create more abnormal cells. This is one of the ways cancer can develop.
Among women with a mutation in the BRCA1 gene, 72 percent will develop breast cancer in their lifetime and 44 percent will develop ovarian cancer, research has found. Among those with a BRCA2 mutation, 69 percent will develop breast cancer and 17 percent will develop ovarian cancer. Among women with a family history of breast cancer, 20 percent of those cancers are related to the BRCA gene.
Certain ethnic and geographic groups are more likely to have BRCA mutations, with Ashkenazi Jews especially likely to have such mutations. Although the risk of such a mutation is 1 in 400 among the general population, it is 1 in 40 among Ashkenazi Jews. The three most common mutations -- two on BRCA1 and one on BRCA2 -- account for 90 percent of the mutations among Ashkenazi Jews and most cases of genetic-related breast cancer in general. Two percent of Ashkenazi women carry one of these three genes.
The at-home test that you mentioned was recently approved by the FDA to measure mutations in one of these three genes. Such testing was previously more difficult to get because of patent issues and insurance coverage, but with this test, patients can pay out-of-pocket to get BRCA testing.
The big caveat is that the test detects only three of the BRCA mutations, meaning that it won't pick up the multitude of other possible mutations in the BRCA genes. These other mutations have to be identified by more involved tests that assess the complete BRCA genes. Nor does it identify mutations beyond the BRCA genes that can increase the risk of breast cancer.
That's not to say it can't be useful for some people. Ashkenazi Jewish women, whom we've established are more likely to have one of these three mutations, would be good candidates for such screening. Not only can the test assess their lifetime risk of breast cancer, a positive test could lead them to take measures to decrease their risk, such as avoiding the use of hormone replacement therapy or oral contraceptives. They could also consider whether to have prophylactic, or preventive, mastectomies.
Women with a close family history of breast cancer, however, would be better advised to undergo complete DNA sequencing of the BRCA genes. This specialized test, ordered by a physician, is more likely to detect other breast cancer-related mutations. In the future, with our greater abilities to quickly test for genetic abnormalities, at-home tests will be more comprehensive. But, for now, this is a good start.
Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles. Send your questions to firstname.lastname@example.org, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.