Geographic and environmental factors associated with melanoma incidence

Berman-Rosa M, Logan J, Ghazawi FM, Le M, Conte S, Netchiporouk E, Mukovozov IM, Cyr J, Mourad A, Miller WH, Claveau J, Salopek TG, Gniadecki R, Sasseville D, Rahme E, Lagacé F, Litvinov IV. Analysis of Geographic and Environmental Factors and Their Association with Cutaneous Melanoma Incidence in Canada. Dermatology. 2022;238(6):1006-1017. doi: 10.1159/000524949. Epub 2022 Jun 9. PMID: 35679838

Increases in annual average temperature, summer UVR, and greenspace were associated with higher expected incidence of Cutaneous Melanoma cases.

Clinical Pearls

• This ecological study investigated the relationship between various geographic and environmental factors and the distribution of Cutaneous Melanoma incidence throughout Canada

• Increases in annual average temperature, summer UVR, and greenspace were associated with higher expected incidence of Cutaneous Melanoma cases

• Higher number of annual heat events together with highest annual temperature and higher average number of annual rain events were associated with a decrease in CM incidence rate

Discussion:

Cutaneous melanoma (CM) is the leading cause of death when considering cutaneous malignancies. The link between ultraviolet (UV) radiation and CM has been well established and previous studies have commented on epidemiologic trends of CM diagnosis throughout Canada geographically. This ecological study aims to examine the relationship between various geographic and environmental factors and the distribution of melanoma incidence across Canada based on the author’s previously analyzed 1992–2010 data.

Melanoma incidence was obtained via the Canadian Cancer Registry (CCR). Environmental data per forward sortation area (FSA) postal code including UV radiation; normalized difference vegetation index; annual highest temperature; absolute number and average length of yearly heat events; annual total precipitation (rain and snow); and the absolute number and average length of events with precipitation (rain and snow) was obtained from the Canadian Urban Environmental Health Research Consortium. This data was correlated with the respective CM incidence employing negative binomial regression model.

Results displayed significant nationwide differences in weather events between areas with a high CM incidence and those with low CM incidence. Specifically, high-incidence FSAs had higher annual average temperature (7.75°C vs. 6.31°C, p < 0.05), higher summer UVR (6,291 J/m2 vs. 6,108 J/m2, p < 0.05), and more surrounding greenspace/vegetation, as measured by the NDVI (index) at a 1,000 m buffer zone. Similar results were seen for regional comparisons, looking at maritime provinces, Southern Ontario, and southern British Columbia areas versus the low-risk FSAs in adjacent regions. Factors associated with a decrease in CM incidence rate included higher number of annual heat events together with highest annual temperature and higher average number of annual rain events.

Overall, the data presented in this study indicates higher general annual temperature (i.e., more pleasant ambient temperature), availability of green spaces, and the UVR index are the three primary environmental/geographic factors associated with CM risk in Canada. The authors present individual behavior and social norms as factors that may be related to these variables and therefore influence sun exposure of individuals. In contrast, higher number of rain and heat events together with the highest annual average temperature observed may tempt the public to stay indoors in air-conditioned facilities or prompt individuals to apply more clothing, as these factors were associated with lower CM incidence rates. Limitations of this study include lack of accounting for Fitzpatrick skin phototypes, differences in cultural/social beliefs, variation in education on skin cancer or travel to different regions.