Description of the Evidence
Factors associated with an increased risk of melanoma
UV radiation exposure
The relationship between UV radiation exposure and cutaneous melanoma is less clear than the relationship between UV exposure and NMSC. In the case of melanoma, it seems that intermittent acute sun exposure leading to sunburn is more important than cumulative sun exposure; such exposures during childhood or adolescence may be particularly important.
Interventions With Inadequate Evidence as to Whether They Reduce Risk of Nonmelanoma Skin Cancer
Sunscreen use and UV radiation avoidance
It is not known if interventions designed to reduce exposure to UV radiation through the use of sunscreens and/or protective clothing or through limitation of exposure time reduce the incidence of NMSC in humans. Some studies have used solar keratoses rather than invasive skin cancer as the study endpoint. It is generally felt that half or more of SCCs arise from solar keratoses. However, nearly half of SCCs occur in clinically normal skin. A longitudinal study has shown that the progression rate from solar keratoses to SCC is about 0.075% to 0.096% per year, or less than 1 in 1,000 per year. Moreover, in a population-based longitudinal study, there was an approximately 26% spontaneous regression rate of solar keratoses within 1 year of a screening examination. Therefore, it is likely that solar keratosis is a poor surrogate endpoint in SCC prevention trials.
One very small randomized placebo-controlled study of a sunscreen (sun protection factor [SPF] 29) was conducted in 53 volunteers who had either clinical evidence of solar keratoses or NMSC. Only 37 of the participants returned for the planned 2-year follow-up (attrition rate of 30%). The rate of new solar keratoses was lower after 2 years in the sunscreen group than in the placebo (base-cream) group (estimated 36% reduction in annual rate, P = .001). Another study showed that regular sunscreen use helps reduce the incidence of solar keratoses and increase remission of existing lesions. In Australia, 588 persons aged 40 years and older who attended a free skin cancer screening clinic and had 1 to 30 solar keratoses were enrolled in a randomized controlled trial (RCT) assessing the effect of regular sunscreen (SPF 17) use on solar keratoses; 431 persons completed the study. Individuals in the sunscreen group developed fewer new lesions and had more remissions of existing lesions than those in the base-cream placebo group. There was an increase of 1.0 in the mean number of solar keratoses in the base-cream group versus a decrease of 0.6 in the sunscreen group (difference = 1.53; 95% confidence interval [CI], 0.81-2.25). The rate ratio of new lesions was 0.62 (95% CI, 0.54-0.71). Furthermore, in the sunscreen group, the development of new lesions and the remission of existing lesions were related to the amount of sunscreen used. Such a relationship was not observed in the base-cream group.