Skin carcinomas are the most frequent malignancies in white populations and exposure to ultraviolet radiation from the sun appears to be a major etiological factor. UV radiation damages DNA which causes mutations in genes which can render skin cells malignant. Variations in genetic background, viz. in pigmentation and repair of damaged DNA, determine susceptibility to the formation of skin carcinomas. Certain types of human papilloma virus (HPV) could raise the susceptibility. Aside of this direct carcinogenic impact, UV irradiation affects the immune system, most notably the cellular immunity against skin carcinomas can be suppressed. Such immune modulatory effects are utilized in the dermatological clinic in phototherapy of skin diseases, most specifically psoriasis, but these immunological effects can also cause “sun allergy” of the skin (“polymorphic light eruption”, PLE). Of general benefit to our health is the UV-driven synthesis of vitamin D3 in the skin, which among other can lead to inhibition of tumor growth.
Figure 1: Squamous Cell Carcinoma (carcinoma spinocellulare)
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