UV-induced immune modulation in the lung niche slows cancer progression.

Ultraviolet radiation has a well-documented local immunosuppressive effect on the skin that can enhance subcutaneous tumor growth; however, its systemic impact on cancer progression in internal organs remains poorly understood. Here, we show that chronic UVB exposure after melanoma metastasis to the lung inhibits metastatic growth and modestly improves survival in mice. In UK Biobank participants, higher solar radiation exposure is positively associated with improved lung cancer survival. Mechanistically, UVB modulates the tumor immune environment: Mass cytometry of CD45 immune infiltrate cells from lung metastases of mice UVB-and sham-irradiated revealed a UVB-induced increase in CXCR2 neutrophils and a reduction in Ly6C inflammatory monocytes, with no changes in regulatory T cells or expression of immune checkpoint molecules. Together, these results highlight a potentially protective role of UVB and solar radiation and provide a rationale for further investigation into UV as a factor that enhances antitumor immunity.