ESR1 and breast cancer: Overall, most PARP inhibitor candidates had TNBC (64 of 729 [8.8% of total cohort]), predominantly those with residual disease after neoadjuvant chemotherapy (54 of 729 [7.4% of total cohort]), while the remaining 37 of 729 PARP inhibitor candidates (5.1% of total cohort) had ER-positive, ERBB2-negative breast cancer.