ABCB5 and melanoma: The ABCB5 mediates chemotherapy drug resistance in stem-like tumor cell subpopulations in human malignant melanoma and is commonly over-expressed in circulating melanoma tumor cells43, together with beta-catenin (CTNNB1), a key regulator of melanoma cell growth44, and with its critical downstream target microphthalmia-associated transcription factor (MITF), which mediates melanocyte differentiation45 (Fig. 5h).