The experimental support for the concept that vitamin D status is of relevance for progression of melanoma and other malignancies was the demonstration of the almost ubiquitous expression (including in melanocytes, melanoma cells, and many immune cells) of both the vitamin D receptor (VDR) and the activating enzyme (vitamin D-1α-hydroxylase, CYP27B1), which converts serum 25-hydroxyvitamin D [25(OH)D] into the biologically active vitamin D metabolite 1,25-dihydroxyvitamin D [1,25(OH)2D] (10, 11). The gene discussed is CYP27B1; the disease is melanoma.