Skin Cancer and Sun Exposure Patterns

Abstract

Introduction: Skin cancers are more prevalent than all other cancers combined. Basal cell carcinoma (BCC) is the most common skin cancer and melanoma is rarer but more lethal. The main environmental risk factor for skin cancer is ultraviolet radiation (UVR) or sunlight. As anatomic sites of melanoma are correlated with the patterns of UVR exposure, examining trends in melanoma incidence by birth year and anatomic site can help clarify if changes in patterns of sun exposure have contributed to the rise in melanoma incidence. The relationships between BCC and UVR may be akin to those of melanoma and UVR with intermittent sun exposure (indicated by sunburns) as more important exposure patterns. However, the magnitudes of the associations between BCC and sunburn occurring at different stages of the life course are not clearly understood. In order to develop and assess effective public health interventions for skin cancer prevention, there needs to be increased understanding of the risk factors, including assessment and development of valid measures of exposure. The overall goal of this project was to identify research gaps and opportunities for skin cancer prevention and to assess measurement tools for use in future research to address the identified gaps. Methods: First, melanoma birth cohort trends in the United States (U.S.) were stratified by sex and anatomic site of the lesion. Poisson regression was used to estimate incident rates of malignant melanoma diagnosed from 1975-2017 from the Surveillance, Epidemiology, and End Results cancer registries restricted to Whites aged 20-84 at diagnosis. Then, a meta-analysis was conducted to quantify the impact of sunburn at different life stages on BCC risk in the general population and identify any gaps in the literature. A systematic literature search was conducted with data extracted by two independent reviewers using standardized forms. Both dichotomous and dose response meta-analysis were conducted. Finally, inter-method reliability of two potential markers of sun exposure (monthly serum vitamin D and melanin difference between skin exposed and unexposed to sunlight) were compared with daily dairies of sun exposure collected over several months among a group of 44 adults in Iowa. Reliability was assessed using Pearson Correlation. Results: Results showed melanomas at all anatomic sites continue to increase for women, while for men, sharp increases across birth cohorts prior to 1944 are not seen after 1945 except for head and neck melanomas. Increase in melanoma incidence varied by sex and anatomic site of the lesion, suggesting changes in UVR may contribute to the increased incidence of melanoma observed across birth cohorts. The meta-analysis of sunburn and BCC risk suggests that sunburn increases the risk of developing BCC for all life stages (childhood, adult, or lifetime) and BCC risk increases with an increase in the number of sunburns. Melanin difference between the upper inner arm and forearm was correlated with recorded minutes of sun exposure when adjusted for sun protection use but correlations were less than 0.60. Serum vitamin D was not correlated with diary recorded minutes of sun exposure, even when adjusted for sun protection use. Discussion: My results suggest changes in UVR exposure patterns over time may be contributing to increased incidence of melanoma in the U.S. The pooled estimates of BCC risk with sunburns from the meta-analysis show risk associated with intermittent sun exposure similar to melanoma. However, more research needs to be conducted quantifying the risk of BCC associated with sunburn occurring in adolescence and adulthood. Examining markers for sun exposure, the correlation with time in the sun indicates melanin difference between skin unexposed and skin exposed to sunlight may be a marker of sun exposure for the past month, while serum vitamin D is not. The low to moderate correlations with melanin difference insinuate more work is needed. The relationship between sun exposure and skin cancer is complex, with suggestion of similar patterns for melanoma and BCC. Melanin measured tanning could be used as an indicator of chronic sun exposure patterns for future sun exposure and skin cancer research.