Limited Independent Follow-Up with Germline Testing of Variants Detected in BRCA1 and BRCA2 by Tumor-Only Sequencing

Introduction: Genomic profiling is performed in patients with advanced or metastatic cancer, in order to direct cancer treatment, often sequencing tumor-only, without a matched germline comparator. However, because many of the genes analyzed on tumor profiling overlap with those known to be associated with hereditary cancer predisposition syndromes (HCPS), tumor-only profiling can unknowingly uncover germline pathogenic (P) and likely pathogenic variants (LPV). In this study, we evaluated the number of patients with P/LPVs identified in BRCA1 and BRCA2 (BRCA1/2) via tumor-only profiling, then determined the germline testing outcomes for those patients. Methods: A retrospective chart review was performed to identify patients with BRCA1/2 variants on tumor-only genomic profiling, and whether they had germline testing. Results: This study found that of 2923 patients with 36 tumor types who underwent tumor-only testing, 554 had a variant in BRCA1/2 (19.0%); 119 of the 554 patients (21.5%) had a P/LP BRCA1/2 variant, representing 4.1% of the overall population who underwent genomic profiling. Seventy-three (61.3%) of 119 patients with BRCA1/2 P/LPV on tumor-only testing did not undergo germline testing, 34 (28.6%) had already had germline testing before tumor-only testing, and 12 (10.1%) underwent germline testing after tumor-only testing. Twenty-eight germline BRCA1/2 P/LPVs were detected, 24 in those who had prior germline testing, and 4 among the 12 patients who had germline testing after tumor-only testing. Conclusion: Tumor-only testing is likely to identify P/LPVs in BRCA1/2. Efforts to improve follow-up germline testing is needed to improve identification of germline BRCA1/2 alterations.