PARP1 and cancer: Previously, reversal mutation of BRCA2, loss of PARP1 protein expression, and overexpression of drug efflux pumps ABCB1 (p‐glycoprotein) and ABCG2 (BCRP) have been linked to acquired resistance to PAPRi in BRCA2 mutant cancer [9, 12, 13, 29, 30].