From the bench to emerging new clinical concepts: Our present understanding of the importance of the vitamin D endocrine system (VDES) for skin cancer.

It is well accepted that growth and differentiation of keratinocytes and other cell types are regulated by 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], the active form of vitamin D. Moreover, growing evidence now indicates that the UV-B-mediated cutaneous photosynthesis of vitamin D [and the consecutive cutaneous production of 1,25(OH)(2)D(3))] represents an evolutionary highly-conserved endocrine system that protects the skin against environmental hazards that may promote skin cancerogenesis, including ultraviolet and ionizing radiation. It is the aim of this review to summarize our present understanding of the cutaneous vitamin D endocrine system (VDES) and its importance for the prevention of skin cancerogenesis.