ABCG2 and breast cancer: Strikingly, an ability of BGJ 398 to inhibit the efflux of chemotherapeutic agents from cancer cells was not limited to Tx-R breast cancer cells and was also observed in the ABC-overexpressing Tx-R cancer subline exhibiting different tissue origin—e.g., Tx-R GIST T-1 cells (Supplementary Figure S1), thereby suggesting the inhibition of ABC-transporters activity as a common mode of action of BGJ 398.