Drug-efflux transporter genes (ABCB1a, ABCB1b, and ABCB2) encoding multidrug resistance protein 1 (MDR1) were found to be highly expressed and exhibited epithelial-to-mesenchymal transition phenotypes in a PARPi resistant cohort in a murine model of BRCA1-mutated breast tumors (81). This evidence concerns the gene ABCB1 and breast neoplasm.