Assessing the effect of environmental and socio-economic factors on skin melanoma incidence: an island-wide spatial study in Gran Canaria (Spain), 2007-2018

Abstract

Introduction: Skin melanoma incidence has risen in the last decades becoming a major public health problem in many regions of the world. Geographic variation of rates is not well understood.

Purpose: To assess the spatial distribution of skin melanoma in Gran Canaria Island (Canary Islands, Spain) and to evaluate the role of environmental, socio-economic, and demographic factors in this distribution.

Methods: We performed a small-area study with disease mapping at the census-tract level (CT) in Gran Canaria between 2007 and 2018. After testing for spatial autocorrelation, we integrated individual-level health data with census-based demographic and socio-economic indicators, and satellite-based environmental data. Finally, we assessed the role of demographic, socio-economic and environmental factors on skin melanoma incidence using a Bayesian analytical framework, with options for non-spatial and spatial random effects.

Results: 1058 patients were diagnosed with invasive skin melanoma in the study period and geolocated to a CT (number of CT in Gran Canaria = 565). We found evidence of global spatial autocorrelation in skin melanoma incidence (Moran's I = 0.09, pseudo p-value = 0.001). A few hotspots were detected, fundamentally in urban northern tracts. A radial pattern of high values was also observed in selected ravines with historical isolation. Multivariable conditional autoregressive models identified urbanicity, percent of females, and a high socio-economic status as risk factors for disease. Solar radiation did not show a significant role.

Conclusion: Urbanicity and a high socio-economic status were identified as the main risk factors for skin melanoma. These associations might reflect differential melanoma susceptibilities or be explained by health inequalities in detection. This study also uncovered high-risk areas in particular ravines. Future targeted research in these regions might help better understand the role of genetic and toxic factors in melanoma pathogenesis.

Keywords: Environment; Epidemiology; Melanoma; Socio-economic factors; Spain; Spatial analysis.

Fig. 1

Choropleth map showing the incidence of skin melanoma in Gran Canaria Island and in the capital city of Las Palmas de Gran Canaria (LPGC) in 2007–2018, at the census-tract level. Incidence presented as Age-adjusted Standardized Incidence Ratios (aSIR) per census tract (CT). An aSIR of 1 in a CT indicates an observed number of cases equal to that expected for the CT in the study period, based on the overall incidence in the island and considering the total population of the CT and its age composition. An aSIR > 1 indicates a higher incidence than expected, and aSIR < 1 a lower incidence than expected. An aSIR of 3 indicates an incidence 3 times higher than expected for the CT

Fig. 2

Cluster maps of skin melanoma incidence showing the type of spatial association between adjacent neighborhoods in Gran Canaria and in LPGC city in 2017–2018. Local Indicator of Spatial Autocorrelation (LISA) cluster map. High–high and low–low indicate clustering of similar values and high–low and low–high indicate spatial outliers. Spatial weights with Queen’s contiguity of first order, with age-adjusted SIR as outcome and significance filter of p < 0.01

Fig. 3

Modeled skin melanoma incidence in Gran Canaria Island and in the city of Las Palmas de Gran Canaria (LPGC) in 2007–2018 at the census-tract level, with the final model. A Fitted values of median aSIR with the Bayesian conditional autoregressive model accounting for fixed and independent random effects. B Lower and upper bounds of the 95% CI for modeled aSIR across the island. aSIR age-adjusted standardized incidence ratios, CI credible interval