Basal cell carcinoma (BCC)

A. Environmental factors 1. Non-Ionizing Radiation – Ultraviolet (UVA & UVB) Two wavelength “types” of UV reach the earth’s surface – UVA (320-400nm) and UVB (290-320nm). Most of the UVB and all UVC are filtered by stratospheric ozone. UVA was initially thought to be noncarcinogenic, but is now thought to be a potent co-carcinogen with UVB. Recently, high dose UVA (as found in tanning beds) has been shown to be carcinogenic in its own right. The carcinogenic effect of sunlight is both as an initiator and promoter of tumors. UV energy is absorbed by DNA, causing DNA methylation, double strand breaks and the formation of thymidine dimers (photochemical damage), which prevent accurate DNA transcription during mitosis leading to mutations.