Those who carry a specific genetic change — a germline BRCA1, BRCA2 or CHEK2 mutation — have at least a twofold increased risk of cancer in both breasts, also called contralateral breast cancer, according to researchers at the Mayo Clinic Comprehensive Cancer Center in Rochester, Minn.
The study of 15,000 women also found that those with germline ATM mutations did not have a significantly elevated risk of cancer in both breasts.
For some carriers of the PALB2 gene, the risk was dependent on other factors. They had a significantly elevated risk of cancer in both breasts if they had estrogen receptor-negative disease, the investigators found.
"These are the first population-based numbers out there for these three genes beyond BRCA1/2," said lead investigator Fergus Couch, a breast cancer researcher at Mayo. "It is also one of the largest studies to provide estimates of contralateral breast cancer risk by age at diagnosis, menopausal status and race/ethnicity in germline mutation carriers."
Study co-author Dr. Siddhartha Yadav, a medical oncologist at the cancer center, said most patients who have breast cancer and carry germline mutations assume they are at high risk of developing cancer in the opposite breast.
A comprehensive assessment of risk based on age, estrogen receptor status, menopausal status and the effect of treatment for initial breast cancer had not been done for even BRCA1/2 carriers, Yadav noted.
"The findings reveal important information that will aid in a personalized assessment of contralateral breast cancer risk in our patients who are germline mutation carriers," Yadav said in a Mayo news release. "Having this level of detail will help guide decisions between patients and their care teams on appropriate screening and steps to reduce the risk for contralateral breast cancer."
Women who were premenopausal had higher risk of cancer in both breasts than those who were postmenopausal when diagnosed, the study authors said. Black women and white women had similar elevated risk for contralateral breast cancer.
"Many women will undergo bilateral mastectomy to reduce the possibility of a second breast cancer," Couch said. "Now we have data to work from when making the decision to remove the second breast, pursue aggressive surveillance or take preventive medication."
The report was published online recently in the Journal of Clinical Oncology.
The American Cancer Society has more on gene mutations and breast cancer.
SOURCE: Mayo Clinic, news release, Jan. 19, 2023