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Complex Relationship Between Sun Exposure and Nonmelanocytic Skin Cancers

Basal cell carcinomas (BCCs) and squamous cell carcinomas (SCCs) have long been associated with cumulative lifetime sun exposure. To evaluate further the relationship between these carcinomas and the timing of sun exposure, these authors conducted two questionnaire studies.

One study compared 226 men with BCCs and 406 control subjects. As expected, patients with BCC had lighter skin color than the controls and freckled easily in childhood. In addition, BCC patients often reported having severe sunburns during childhood. The relationship between sun exposure and the development of BCC was more complex than previously thought. Patients with BCC reported more time spent in the sun as adolescents than did controls, but did not have higher cumulative recreational sun exposures. In fact, there was an inverse relationship between cumulative lifetime sun exposure and risk for developing BCC.

The other study compared 225 patients with SCCs and 573 control subjects. Patients with SCC had lighter skin than controls, were more likely to have red hair, and freckled easily. These patients were also more likely to burn and to not tan. Those of Northern European descent were also at increased risk. Again, the relationship between sun exposure and development of carcinoma was more complex than previously reported. Unlike BCC, there was no relationship between SCC and recreational sun exposure during adolescence. There was also no association between risk for SCC and cumulative lifetime sun exposure. However, increased occupational sun exposure in the 10 years before diagnosis was strongly associated with an increased risk for SCC.

Comment: These results are at odds with most previous studies attempting to correlate sun exposure with the development of carcinoma. It has been widely accepted that basal cell and squamous cell carcinomas are related quite simply to skin type and cumulative lifetime sun exposure. These studies suggest that timing of solar exposure may be more important than cumulative lifetime exposure, with BCCs more closely associated with intense exposure early in life and SCCs more closely associated with short, intense exposures shortly before the onset of the neoplasm.

It should be cautioned, however, that these studies suffer from several methodological shortcomings. First, the data may not be all that reliable because they are based on responses to a questionnaire. Second, the studies are retrospective, analyzing only patients who already had developed neoplasms. Further, patients were from the relatively high latitude of Alberta, Canada, where they may not receive the same amounts of UV irradiation as persons living at lower latitudes. Finally, the number of patients questioned was relatively small compared with the vast numbers of patients who have these tumors.

— BR Smoller

Published in Journal Watch Dermatology April 1, 1995

Citation(s):

Gallagher RP et al. Sunlight exposure, pigmentary factors, and risk of nonmelanocytic skin cancer. 1. Basal cell carcinoma. Arch Dermatol 1995 131 157-163.

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Gallagher RP et al. Sunlight exposure, pigmentation factors, and risk of nonmelanocytic skin cancer. 2. Squamous cell carcinoma. Arch Dermatol 1995 131 164-169.

• Medline abstract (Free)