Successful BRCA2 Mutation Detection via Tissue-Based Gene Panel Testing in Post-bone Marrow Transplant Breast Cancer:...

BRCA1 and BRCA2 (BRCA1/2) mutation screening is recommended for patients with advanced breast cancer or early breast cancer suspected to have hereditary origins based on family history or tumor characteristics. Blood-based testing is the standard approach, but it is not feasible in patients who have undergone bone marrow transplantation due to the replacement of blood cells with donor-derived cells. We report a case of a patient who, following bone marrow transplantation, required an alternative to blood-based germline BRCA1/2 screening. A germline BRCA2 mutation was inferred through tissue-based gene panel testing on a tumor sample, using variant allele frequency analysis. This approach allowed the initiation of targeted therapy with poly(ADP-ribose) polymerase (PARP) inhibitors, resulting in sustained progression-free intervals. This case demonstrates the potential of tissue-based gene panel testing to identify actionable germline mutations in breast cancer patients when blood-based testing is not feasible, thereby expanding therapeutic options in complex clinical scenarios.