BRCA1 and breast cancer: These studies will be especially relevant for trials incorporating poly ADP ribose polymerase inhibitors, a drug class of specific interest due to its preferential use in BRCA1 and BRCA2 mutation carriers, known dose‐limiting hematologic toxicities, and association with therapy‐related myeloid neoplasms.22, 23 Lastly, given that G‐CSF support is a required component for safe delivery of many modern breast cancer regimens, we were unable to rule out differences in toxicities by mutation status in the absence of this agent, but this is likely not clinically relevant.