The latitudinal gradient of cancer morbidity, in particular for breast cancer, has been known for ¾ century to correspond inversely with ambient sunlight and its mechanism has been attributed for the past nearly 4 decades to sunlight's production of cancer-inhibiting vitamin D₃ in the skin. Makarova et al (page 383) have tested the anti-cancer effects of ultraviolet irradiation and D₃ in a murine cancer model in which large T antigen expressed in the mammary gland drives fatal mammary gland carcinogenesis. They have found that in this model UVR does delay and reduce tumor progression, that vitamin D₃ administration, whether given systemically or applied topically to the skin, has no such effect, and that the effects of UVR persist in mice unable to produce D₃ on exposure to UVR. The authors suggest that identification of the non-D₃, UV-induced molecule that transmits the anti-cancer effect from the skin to the mammary gland might uncover novel approaches for prevention of extra-cutaneous human cancer. On the cover is an image of a murine mammary gland with DCIS, treated with UV, and stained to display (black) expression of the large T antigen.