PGP and cancer: Further insight into the function of sphingolipids, ABCB1/P-gp upregulation, and multidrug resistance is available in work by Lee and Kolesnick [150], who postulated that increased sphingomyelin content, developing early in some cancers, recruits and functionalizes plasma membrane ABCB1/P-gp, conferring a state of partial multidrug resistance that later brings glycosphingolipids into the picture.