Vitamin D and cancer: antineoplastic effects of 1 alpha,25(OH)(2)-vitamin D-3. The hormonal form of vitamin D, 1 alpha,25(OH)(2)-vitamin D-3 (1 alpha,25(OH)(2)D-3), in addition of playing a central role in the control of calcium homeostasis in the body, regulates the growth and differentiation of different cell types, including cancer cells. At present several epidemiologic and clinical studies investigate the effect of the hormone in these cells due to the interest in the therapeutic use of 1 alpha,25(OH)(2)D-3 and analogues with less calcemic activity for prevention or treatment of cancer. This review describes vitamin D endocrine system, its mechanism of action, its antineoplastic activity and provides information about the latest advances in the study of new hormone analogues with less calcemic activity for cancer treatment.