The increased expression of the ATP‐dependent efflux pump ABCB1 (MDR1), which encodes the membrane drug efflux transporter P‐glycoprotein, might readily export PARP inhibitors from tumour cells and lead to resistance to the PARP inhibitors olaparib or rucaparib but not to veliparib or AZD2461, both of which are poor P‐glycoprotein substrates.29, 99, 100 However, this resistance can be reverted using the ABCB1 inhibitors verapamil, elacridar and tariquidar.101. Here, PARP1 is linked to neoplasm.