Actionable co-alterations in breast tumors with pathogenic mutations in the homologous recombination DNA damage repair pathway.

HR-MT was common across breast cancer subtypes and co-occurred more frequently with markers of response to immunotherapy (MSI-H/dMMR, TMB) compared to HR-WT tumors. Mutations were identified in both HR-MT and HR-WT tumors that suggest other targets for treatment. Clinical trials combining HRD-targeted agents and immunotherapy are underway and could be enriched through comprehensive molecular profiling.