The first discovery of at least 48distinct ABC human transporter genes responsible for drug efflux wasmultidrug resistance protein 1 (MDR1), also known as ATP-binding cassettesubfamily B member 1 (ABCB1) or permeability glycoprotein (P-gp).3,4 MDR cancers commonly overexpressP-gp,5 either innately, or as a consequenceof repeated treatment with chemotherapy; this makes therapies whichinhibit or act orthogonal to drug efflux particularly valuable.6−8. This evidence concerns the gene ABCB1 and cancer.