Cancer cells may acquire the overexpression of ABC transporters for the efflux of chemotherapeutic drugs, most notably P-glycoprotein 1 (Pgp, also known as ABCB1, MDR1 or multidrug resistance 1), and many ADC payload molecules are substrates for these transporters that have a broad substrate specificity for hydrophobic molecules [124]. Here, ABCB1 is linked to cancer.