Purpose: We conducted this systematic evidence review of five key questions to assist the U.S. Preventive Services Task Force (USPSTF) in updating its 2003 recommendation on behavioral counseling to prevent skin cancer (melanoma, basal cell carcinoma, and squamous cell carcinoma).
Data Sources: We first conducted a comprehensive search for systematic reviews from 2001 until March 2008. Using three existing systematic reviews, we developed separate searches for each key question. We searched MEDLINE and the Cochrane Central Register of Controlled Trials from 2001 through December 2008 for key questions 1 to 3; from the end search dates of existing systematic reviews through December 2008 for key question 4 (if no existing systematic review was identified, we searched from 1966 through December 2008); and from 1966 through December 2008 for key question 5. We also obtained articles from outside experts and by reviewing bibliographies of relevant articles and existing systematic reviews.
Study Selection: We reviewed a total of 5,387 abstracts and 324 complete articles. There were a total of 57 unique studies included in this review: 10 examining the effectiveness and harms of counseling interventions; 32 examining the epidemiologic link between sun exposure, indoor tanning, or sunscreen use and skin cancer; and 16 examining the potential harms of sun-protective behaviors.
Data Extraction: Two investigators independently reviewed abstracts and articles against a set of a priori inclusion criteria, and also independently critically appraised each study using design-specific quality criteria based on USPSTF methods and the Newcastle-Ottawa quality criteria for cohort and case-control studies. One investigator abstracted data from included studies into evidence tables and a second investigator checked the data.
Data Synthesis: We found 10 fair-or good-quality randomized controlled trials (RCTs) that examined the impact of primary care relevant skin cancer counseling interventions on sun-protective behaviors, two of which examined community-based interventions with a component of counseling in primary care. In adults (n=6,225), primary care relevant counseling with computer support increased composite scores measuring sun-protective behaviors at 6 to 24 months. In young adults (n=563), brief appearance-focused behavioral interventions decreased normative indoor tanning behaviors at 6 months and decreased ultraviolet (UV) exposure, as objectively measured by skin pigmentation at 12 months. In young adolescents (n=819), primary care counseling with computer support, similar to those used in adults, decreased midday sun exposure and increased sunscreen use at 12 and 24 months. In parents of newborns (n=728), primary care counseling integrated into sequential well-child care visits increased composite scores measuring sun-protective behaviors at 36 months. Successful interventions ranged from single low-intensity interventions (e.g., 15-minute single session, booklet, video) to multiple in-person or phone-based counseling. No significant harms, including physical activity and sedentary behaviors, were reported in these trials.
We found mainly fair-quality cohort and case-control studies examining the relationship between sun exposure and skin cancer (11 studies for squamous cell and basal cell carcinoma, 18 studies for melanoma). We found that increasing intermittent (or recreational) sun exposure is associated with an increased risk for squamous cell and basal cell carcinoma and melanoma. This association is more consistent in studies with the timing of intermittent sun exposure in childhood. Fewer studies examined the association of total and chronic (or occupational)sun exposure. These studies do not suggest a strong association between total or chronic sun exposure and skin cancer. However, some evidence suggests that total sun exposure in childhood is associated with an increased risk for melanoma and occupational sun exposure may be associated with a decreased risk for melanoma.
We found very few studies that examined the relationship between indoor tanning and risk for squamous cell or basal cell carcinoma, after adjusting for all important confounders. Results generally suggest no association. However, a slightly larger body of higher quality evidence suggests that “regular” or “early” use of indoor tanning devices may increase the risk for developing melanoma. Most of these studies used crude measures of indoor tanning device exposure.
Based on one fair-quality trial, regular sunscreen use may prevent squamous cell carcinoma but not basal cell carcinoma. Case-control studies that suggest sunscreen use reduces the risk for basal cell carcinoma have major limitations. Based on five fair-quality studies, sunscreen use has no clear protective or harmful effect on the risk for melanoma, although the case-control studies examining this risk have major limitations.
Few harms were found in 16 fair-quality studies examining the potential harms of sun-protective behaviors. In school-aged children (n=1,615), sun-protective behaviors do not increase risk for sedentary behaviors or increase in body mass index. Based on three good-quality trials (n=516), use of sunscreen with a higher sun protection factor can increase duration of intentional sun exposure in sun bathers. However, three other fair-to good-quality trials (n=2,520) suggest that sunscreen use in general does not appear to increase sun exposure in adults or children. In adults (n=153), sunscreen use does not lead to vitamin D deficiency. Ina cohort of women living at high latitudes (n=2,016), however, those who avoided direct sun exposure were at risk for vitamin D deficiency during the winter and spring months. Four of seven fair-or good-quality studies that examined the relationship between sun exposure and risk for cancer suggest that sun exposure in predominantly white persons may be inversely related to risk for advanced breast and prostate cancer and non-Hodgkin lymphoma, after adjusting for well-established risk factors. However, none of these trials adjusted for dietary vitamin D intake or measured vitamin D status.
Limitations: The main limitations for the trial evidence supporting counseling to prevent skin cancer are the small number of trials in children and the unclear clinical significance of small changes in composite scores measuring sun-protective behaviors. Major concerns about the internal validity of the observational literature include the complex nature of measuring sun exposure and sunscreen use, in consistent and inadequate adjustment for important confounders, and use of study designs complicated by recall bias. Results from the observational literature examining indoor tanning device use and sunscreen use may not be applicable to today’s products due to changes in indoor tanning devices and sunscreens over time. Most of the counseling trials and all of the epidemiologic studies include exclusively or predominantly white populations.
Conclusions: A limited number of RCTs suggest that primary care relevant behavioral counseling can minimally increase sun protection composite scores in adults and their newborns, decrease indoor tanning and objectively measured pigmentation in college students, and decrease midday sun exposure and increase sunscreen use in young adolescents. The clinical significance of small changes in sun protection composite scores is unclear. Many of the counseling interventions incorporated computerized support that could generate tailored feedback. Evidence, mostly from case-control studies, suggests that intermittent sun exposure, especially in childhood, is associated with an increase drisk for skin cancer. Regular sunscreen use can prevent squamous cell carcinoma, but it is unclear if it can prevent basal cell carcinoma or melanoma. Therefore, behavioral counseling to promote skin cancer prevention should focus on improving multiple behaviors to reduce UV exposure and not improving sunscreen use alone. There is some evidence to suggest that regular and early use of indoor tanning devices may increase the risk for melanoma. However, sunscreen and indoor tanning technologies have changed substantially over the past 20 to 30 years.