Comprehensive Germline Multigene Panel Testing Changes Clinical Care For Patients With Breast Cancer: Untapped Clinical Utility And Parp Inhibitor Trial Eligibility.

1583 Background: HBOC testing guidelines were established to identify patients with clinically actionable variants and limit economic burden. We report the impact of germline results on health outcome based on clinical decision making and treatment interventions, regardless of guidelines, in a multi-center registry. Methods: 20 community-based and academic participated in an IRB approved registry. Patients with breast cancer were tested with an 80-gene panel; clinical information was collected. Results: Data on 912 patients has been analyzed to date. 50.5% met NCCN criteria; 49.5% did not. Pathogenic/likely pathogenic (P/LP) germline mutations were found in 8.65% of patients. Of all patients with P/LP findings, 85% had variants in cancer-risk genes with established management recommendations and 80% had germline variants conferring eligibility for clinical trials and precision medicine-based cancer treatments, such as PARP inhibitors. For 62% of patients with P/LP germline mutations, clinicians reported results impacted patients’ health outcome. And for 69%, results impacted the health outcome of patients’ relatives. There was no significant association between BRCAPRO scores and patients having a P/LP finding, whether in BRCA1/2 alone (p = 0.42) or for any cancer gene (p = 0.57). Physician reported impact on patient outcome associated significantly with the presence of P/LP germline findings (p < 0.00001). There was no significant difference in the clinician reported clinical utility of variants of uncertain significance (VUS) compared to negative results (p = 0.467). Conclusions: Comprehensive panel testing of breast cancer patients impacts physician assessed patient outcomes and informs changes in surgical treatment strategy, medical therapies and proactive screening. The data suggest that BRCAPRO calculators are poor predictors of germline presence of P/LP findings. Physicians in this study demonstrate the ability to discern the clinically actionable value of P/LP mutations from non-actionable VUS. Multigene panels impact breast cancer patient care by identifying precision medicine treatment interventions, and guiding long-term medical management and preventive surveillance for patients and family members.