Does mainstream BRCA testing affect surgical decision-making in newly-diagnosed breast cancer patients?

Background: Germline pathogenic variants mutations) in the BRCA1 and BRCA2 genes cause an increased risk of breast cancer and ovarian cancer. Mainstream cancer genetic testing (MCG) was introduced for breast cancer patients in our unit in 2013. Non-geneticist clinicians have been trained to offer genetic testing during initial treatment planning. We assessed the impact of timely test results on surgical decision-making. Methods: Women who had undergone mainstream genetic testing for breast cancer between September 2013 and September 2018 were identified from a prospective database. Surgical data were collected retrospectively. Results: 580 eligible women had mainstream genetic testing. For 474 this was their first breast cancer diagnosis. The median age was 46 years (interquartile range (IQR) 38–57). The indications were: age ≤45 years for 233 (49%); triple negative disease for 192 women (40.5%); bilateral breast cancer age <60 for 39 (8%) and other for 72 (14%) women. The median time for test initiation to result was 18 days (IQR 15-21). 302 (64% received results before surgery. 88% of those found to have a BRCA mutation before surgery opted for bilateral mastectomy (compared to 5% with BRCA wild type). An additional 106 patients had a new diagnosis on a background of previous treatment. Of these all with a pathogenic variant chose bilateral mastectomy. Conclusion: Timely BRCA gene testing influences surgeons’ and patients’ choice of surgery. It reassures women with a negative result and allows those with a positive result to take an active decision about the management of their future risk.