The L-phenylalanine prodrug melphalan (Fig. 4A), a widely used anticancer drug for the treatment of ovarian cancer and multiple myeloma, inhibited the uptake of L-leucine into human MDA-MB-231 breast cancer cells (81), T24 human bladder carcinoma cells (82) and in hLAT1 expressing Xenopus oocytes (16) providing evidence of binding to LAT1. This evidence concerns the gene SLC7A5 and breast carcinoma.