Recommendations for Clinical Molecular Laboratories for Detection of Homologous Recombination Deficiency in Cancer: A Joint Consensus Recommendation of the Association of Molecular Pathology, Association of Cancer Care Centers, and College of American Pathologists.

Homologous recombination deficiency (HRD) is a genomic feature present in some malignant neoplasms and is attributed to the failure of the homologous recombination repair pathway. Tumors with an HRD-positive status may have a distinct prognosis and/or response to therapies, including poly (ADP-ribose) polymerase inhibitors. The Association for Molecular Pathology assembled an expert panel to examine current practice and perform a scoping review of the medical literature pertaining to the molecular detection of HRD in the clinical setting. The expert panel examined the following topics: components of existing and proposed HRD and genomic instability biomarkers (including mutational signatures, loss of heterozygosity, mutations in homologous recombination repair-associated genes, and epigenetic silencing of RAD51C, BRCA1, or BRCA2); technical considerations for identifying genomic scars from tumor and germline next-generation sequencing results; guidelines on interpretation and caveats when reporting assessments of genomic instability and HRD scores; and the clinical significance of HRD. The panel formulated a set of expert consensus opinion recommendations regarding HRD assay design and validation to guide laboratories in developing HRD tests to ensure high-quality and reproducible results.