Clinical signs of photodamage are associated with basal cell carcinoma multiplicity and site: a 16-year longitudinal study

Although sun exposure is known to be associated with basal cell carcinoma (BCC), it is not known what determines multiple occurrences of BCCs among sporadically affected individuals or why BCCs develop on uncommonly sun-exposed body sites like the trunk. In a prospective community-based skin cancer study in Queensland, Australia, we studied all participants who experienced a histologically confirmed BCC from 1992 to 2007. Sun exposure history was monitored, and dermatologists documented phenotype at baseline and signs of photodamage over the study period. Anatomic sites of all incident BCCs were recorded. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated using logistic regression. Of 401 participants who developed a new BCC during the 16 years of follow-up, 232 (58%) developed more than 1. Male sex (OR = 2.5, 95% CI 1.5-5.3) and age 60 or over (OR = 4.2, 95% CI 1.5-11.8) but not skin type were associated with highest BCC counts among those affected. Participants with high numbers of solar keratoses were most likely to experience the highest BCC counts overall (OR = 4.3, 95% CI 1.4-13.5). Moreover, occurrences of BCC on the trunk (OR = 3.3, 95% CI 1.4-7.6) and on the limbs (OR = 3.7, 95% CI 2.0-7.0) were strongly associated with high numbers of solar keratoses on these sites, respectively. Among those newly affected by BCC, chronic cutaneous sun damage predicts those who will be affected by more than 1 BCC, while chronic sun damage on the trunk and limbs predicts BCC occurrence on the trunk and limbs, respectively.