What is the role of radiation exposure in the etiology of basal cell carcinoma (BCC)?

Updated: Mar 02, 2020
  • Author: Robert S Bader, MD; Chief Editor: William D James, MD  more...
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Answer

Sunlight, particularly long-term exposure, is the most frequent association with development of BCC; risk correlates with the amount and nature of accumulated exposure, especially during childhood. Patient geographic location affects the risk of developing skin cancer. A latency period of 20-50 years is typical between the time of ultraviolet (UV) damage and BCC clinical onset.

The prevalence of BCC increases in areas of higher altitude and in areas of lower latitude. The incidence of BCC is rising, potentially because of atmospheric changes and the increased popularity of sunbathing.

Radiation exposure that contributes to BCC development may also include tanning booths and UV light therapy. Both short-wavelength UVB radiation (290-320 nm, sunburn rays) and longer wavelength UVA radiation (320-400 nm, tanning rays) contribute to the formation of BCC. UVB is believed to play a greater role in the development of BCC than UVA, however, and is the primary agent responsible for most skin cancer. [31]

UVB and UVC can modify unsaturated chemical bonds of nucleic acids, which may lead to mutations. UVC does not penetrate the atmospheric ozone layer. The UVA spectrum is absorbed by melanin and, through free-radical transfer, affects cellular deoxyribonucleic acid (DNA). Mutations caused by UV radiation typically include cytosine (C) to thymine (T), or CC to TT, translocation. This process can cause activation of oncogenes or inactivation of tumor suppressor genes, leading to tumor initiation and progression. [32]

The skin can repair superficial damage, but the underlying cumulative damage remains, including DNA damage. The damage worsens with each successive sun exposure, causing a lifetime progression. [33]

In a 2012 systematic review and meta-analysis of 12 studies with 9328 cases of non-melanoma skin cancer, Wehner et al found that indoor tanning was associated with a significantly increased risk of both basal and squamous cell skin cancer. The risk was highest among users of indoor tanning before age 25. The authors estimate that the population attributable risk fraction in the United States is 8.2% for squamous cell carcinoma and 3.7% for basal cell carcinoma, corresponding to more than 170,000 cases of non-melanoma skin cancer annually caused by indoor tanning. [34] In another 2012 study of 376 patients with basal cell carcinoma and 390 control patients with minor benign skin conditions, indoor tanning was strongly associated with early-onset basal cell carcinoma, particularly in women. [35]

X-ray and Grenz-ray exposure are also associated with basal cell carcinoma formation.


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