Impact of Multigene Panel Testing on Surgical Decision Making in Breast Cancer Patients.

BACKGROUND: With the advent of multigene panel testing for breast cancer patients, germline mutations with unknown association with cancer risk, known as variants of uncertain significance (VUS), are being increasingly identified. Some studies have shown higher rates of contralateral prophylactic mastectomies (CPM) in these patients, despite lack of evidence to support this intervention. We analyzed surgical choices in patients who were identified to have VUS. STUDY DESIGN: A retrospective review was performed of patients with triple-negative breast cancer treated at a single institution after multigene panel tests became available (September 1, 2013 to February 28, 2017). Rates of genetic testing, results of testing, and surgical decision making were evaluated. Chi-square or Fisher's exact test was used to compare categorical variables. A p value <0.05 was considered statistically significant. RESULTS: There were 477 triple-negative breast cancer patients identified; 331 met established criteria for genetic testing and 226 (68.3%) underwent genetic testing (multigene panel, n = 130 and BRCA1/2 testing, n = 96). All of them received risk-appropriate genetic counseling and follow-up. Of these, 29 (12.8%) patients had pathogenic mutations in BRCA1/2 or PALB2 (Mut+), 42 (18.6%) had VUS (VUS+), and 155 (68.6%) had no mutations identified (Mut-). Variants of uncertain significance in 6 of 42 patients (14.3%) were later reclassified as normal variants. Eighty-eight percent of Mut+ patients underwent CPM compared with 20.1% of Mut- and 21.4% of VUS+ patients (p < 0.001 for both). Rates of CPM were not significantly different between VUS+ and Mut- (p = 0.37). Multigene panel testing detected pathogenic mutations in non-breast cancer-associated genes in 6 patients, with significant management implications. CONCLUSIONS: When combined with risk-appropriate genetic counseling, detection of VUS did not lead to excessive CPM in this cohort of triple-negative breast cancer patients. Furthermore, panel testing detected mutations in non-breast cancer-associated genes, which had significant implications on management and outcomes.