Abstract
Homologous recombination repair deficiency (HRD) occurs in approximately 10% of breast tumors and represents a major targetable vulnerability across multiple cancer types. Impairment of the homologous recombination DNA repair pathway — arising through somatic and germline mutations in homologous recombination repair genes, epigenetic mechanisms, and transcriptomic changes — leads to genomic instability and a reliance on error-prone repair mechanisms. Poly (ADP-ribose) polymerase (PARP) inhibitors harness the synthetic lethality of HRD and PARP inhibition, with current approvals encompassing both early-stage and advanced breast cancer in patients with germline BRCA1/2 (gBRCA1/2) mutations. However, emerging evidence suggests efficacy of PARP inhibitors beyond gBRCA1/2-mutated breast cancer to tumors with other homologous recombination repair defects that confer a “BRCAness” phenotype. This Review examines opportunities to broaden the use of PARP inhibitors in breast cancer and underscores the importance of innovative biomarkers, combination strategies, and next-generation agents to maximize therapeutic impact.
Authors
Charlotte S. Walmsley, Adela Rodriguez, Panagiotis A. Konstantinopoulos, Geoffrey I. Shapiro, Sara M. Tolaney, Judy E. Garber, Filipa Lynce
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Copyright © 2026 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)