Background and objective: Basal cell carcinoma (BCC) is the most common of all cancers. Ultraviolet radiation is the major etiologic agent in the pathogenesis of BCC, but there is not a straightforward relationship between cumulative exposure and risk. A high proportion of lesions arise on the trunk, which is generally much less exposed to the sun than the head, the major site affected. We tested the hypothesis that the phenotypic determinants and patterns of sun exposure that give rise to BCC on the head and trunk vary in a way that explains the anomalous site distribution.
Methods: The study was set in the context of the Nambour Skin Cancer Study, a community-based follow-up study among 1621 participants with virtually complete ascertainment of BCCs between 1992 and 2004. We compared phenotypic and sun exposure characteristics of participants who developed a first BCC of the head or trunk with those of participants who had no diagnosis of BCC.
Results: BCCs of the trunk were more likely to occur in men; they also occurred at a younger age than BCCs of the head. There was a positive association between sun sensitivity and BCC of the head that was absent for BCC of the trunk. A high number of solar keratoses conferred a greater than 3-fold risk for BCCs of both the head and the trunk. BCCs of the trunk had a particularly strong association with the number of reported sunburns and solar lentigines on the trunk, whereas many lentigines conferred a greater than 3-fold risk of truncal BCC compared with a 50% increased risk of BCC of the head.
Limitations: The relatively small numbers of tumors may have limited our ability to detect statistically significant differences.
Conclusions: BCCs of the trunk are the result of overexposure of the sensitive basal cells of the epidermis to ultraviolet radiation. This may result from acute intense exposures sufficient to cause sunburn among people whose ability to tan makes the skin of their face generally less susceptible to the carcinogenic effects of ultraviolet radiation.