VDR and neoplasm: The first one is the most studied anti-tumor mechanism of vitamin D. When activated by calcitriol, the phosphorylated nuclear VDR forms homodimers or heterodimers VDR-RXR with one of the retinoid X receptors (RXR), then the calcitriol-VDR-RXR complex translocates into nucleus and attaches to the vitamin D response elements (VDREs) in the promoters of target genes, causing the recruitment of co-activators or co-repressors to regulate gene expression in target cells [28, 29].