Heliovaccination: Solar mediated immunity against cancer.

The protective effect of ultraviolet (UV) light against a host of malignancies is well characterised. It was recognised by WHO in their 2006 publication on the global burden of UV-mediated disease. The mechanism by which this oncoprotective effect occurs remains unclear. Vitamin D has been mooted as a potential mediator. However, the evidence does not support this. I suggest that UV irradiation of the skin produces nascent malignant and premalignant cells with associated generic tumor-specific antigens. These are eliminated by immunosurveillance resulting in adaptive immunity. The clonal expansion of these immune cells protects against tumors in other viscera, effectively immunising the host. The evidence for this "heliovaccination" is very strong. Childhood UV exposure protects against cancer in adulthood. Tumor naïve individuals possess anti-tumor antibodies. Antigen-presenting cells mobilise to the skin following specifically UVB skin irradiation. It is time to rethink the link between UV light and cancer.