Ultraviolet Radiation Inhibits Mammary Carcinogenesis in an ER-Negative Murine Model by a Mechanism Independent of Vitamin D3

Three decades ago, the Garlands postulated that vitamin D₃ produced in the skin by ultraviolet radiation (UVR)-induced conversion of 7-dehydrocholesterol to pre-D₃ has anticancer effects, thus triggering more than 9,500 publications on D₃ and cancer. Here, we report that UVR treatment of transgenic mice of the well-established C3(1)/SV40 Tag mammary cancer model significantly inhibits both autochthonous carcinogenesis and allograft tumor growth, but in contrast neither dietary nor topical D₃ influences mammary carcinogenesis in this specific mouse model. Furthermore, UVR's inhibitory effects occur irrespective of whether or not the treatment increases circulating D₃ in the mice. The inhibitory effect of UVR on autochthonous tumors occurs at or before the stage of ductal carcinoma in situ. Our studies indicate clearly that UVR can exert D₃-independent anticancer effects in C3(1)/SV40 Tag mice. Therefore, supplemental D₃ may not mimic all possible beneficial effects of UVR, and uncovering non–D₃-mediated mechanisms of UVR tumor inhibition may lead to novel strategies for cancer prevention. Cancer Prev Res; 11(7); 383–92. ©2018 AACR.

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