Spatial epidemiology of skin cancer in Iran: separating sun-exposed and non-sun-exposed parts of the body

Background Skin cancer is among the most common cancer types with an increasing global trend of incidence rate. This study explores the spatial distribution of skin cancer, considering body sites exposed and not exposed to sunshine separately. Methods We used 4302 skin cancer cases recorded by Fars Cancer Registry in south-western Iran for over 6 years (2011-2017). The variables included in the study were patients' residence address, gender, age, report date, and final topographical code. The patients' addresses were geocoded to the counties of the study area. Skin cancer sites were categorized based on sun exposure in male and female cases. We used the empirical Bayesian smoothing approach to smooth the skin cancer incidence rate at the county level to remove any potential population size bias. Finally, Anselin's Local Moran's Index and Getis Ord G* were used to identify the clustered and high-risk skin cancer geographical areas. Results The incidence rates had an increasing trend from 14.28 per 100,000 people in 2011 to 17.87 per 100,000 people in 2016, however, it was decreased to 13.05 per 100,000 people in 2017. Out of 4302 patients with skin cancer, 2602 cases (60%) were male. The cancer cumulative incidence rate in males and females who were not exposed to sunshine was 7.80 and 14.18 per 100,000, respectively. The rates increased to 86.22 and 48.20 in males and females who were exposed to the sun. There were some high-risk spatial clusters of skin cancer in the study area. Further investigations are required to identify the underlying cause of the formation of these clusters. Conclusions Patients exposed to sunshine, especially among the male group, experienced much higher rates of cancer occurrence as compared to unexposed individuals. With a heterogeneous spatial pattern, hotspots were identified in non-sun-exposed and sun-exposed categories in the study area. Researchers and policymakers can significantly benefit from the spatial analyses of skin cancer incidence. These analyses can provide useful and timely prevention policies as well as tailored monitoring techniques in high-risk regions.

Automated summary

This study investigated the spatial distribution of skin cancer in south-western Iran and found that patients exposed to sunshine, especially males, had significantly higher rates of cancer occurrence. Through geographic spatial analysis, high-risk areas and clusters of skin cancer cases were identified.