The role of UV radiation in the development of basal cell carcinoma.

Basal cell carcinoma (basalioma, BCC) is undoubtedly the most common malignant skin cancer and the most common human malignancy in general, with the continuous increase in its incidence. BCC is generally a disorder of white individuals, especially those with fair skin. UV radiation is the most important risk factor in the development of BCC. Short-wavelength UVB radiation (290-320 nm, sunburn rays) is believed to play a greater role in BCC formation than long-wavelength UVA radiation (320-400 nm, tanning rays). A latency period of 20-50 years is typical between the time of UV damage and the clinical onset of BCC. Therefore, in most cases BCC develops on chronically sun-exposed skin in elderly people, most commonly in the area of head and neck. UVB radiation damages DNA and its repair system and alters the immune system resulting in a progressive genetic alterations and formation of neoplasm. UV-induced mutations in the TP53 tumor-suppressor gene have been found in about 50% of BCC cases. The mutations that activate the Hedgehog intercellular signaling pathway genes, including PTCH, Sonic hedgehog (Shh) and Smoothened (Smo) play a significant role in cutaneous carcinogenesis. Epidemiologic studies demonstrate the higher incidence of the BCC in more equatorial latitudes than in polar latitudes. Other risk factors for the development of BCC include sun bed use, family history of skin cancers, skin type 1 and 2, immunosuppression, previous radiotherapy, and chronic exposure to toxic substances such as inorganic arsenic. Although rarely metastatic, its malignant nature is sometimes emphasized by the local tissue destruction, disfigurement, and even death if left untreated. Due to extremely high incidence of BCC medical professionals should be aware of the importance of the public education on the etiology of this tumor and the importance of the UV protection.