Blocking CCL5 successfully alleviated PARPi-induced fibroblast activation and sensitized PARPis in OC and BRCA1/2-mutant breast cancer xenograft models, indicating that potential strategies to curb fibroblast activation, including neutralizing CCL5, facilitate augmenting the efficacy of PARPis in OC and BRCA1/2-mutant breast cancers. This evidence concerns the gene BRCA1 and breast cancer.