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

and () 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 screening. A germline 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.