ATP-binding cassette sub-family B member 5(ABCB5) is a plasma membrane-spanning protein. ABCB5 is principally expressed in physiological skin and human malignant melanoma. ABCB5 has been suggested to regulate skin progenitor cell fusion and mediate chemotherapeutic drug resistance in stem-like tumor cell subpopulations in human malignant melanoma. It is commonly over-expressed on circulating melanoma tumour cells. Furthermore, the ABCB5+ melanoma- initiating cells were demonstrated to express FLT1 (VEGFR1) receptor tyrosine kinase which was functionally required for efficient xenograft tumor formation, as demonstrated by shRNA knockdown experiments.