Incidence of skin cancers among population exposed to geothermal hot water while bathing and washing

Background/Purpose: Studies on populations in volcanic/geothermal areas in Iceland showed increased incidence of all cancers, breast, prostate cancer, and basal cell carcinoma of skin (BCC). The aim was to study the risk of skin cancers according to morphology and point of origin in the combined populations of previous studies. Methods: Cohort from census included information on personal identifier, age, gender, residency, education, and housing. The follow-up from 1981 to 2010 was based on record linkage of 74,806 individuals, initially 5-64 years of age, with nation-wide death and cancer registries. The exposed population was from communities located on volcanic soil with geothermal hot-water supply generated from geothermal wells since 1972. Two reference populations were from communities located on soil with different degree of volcanic/geothermal activity, without old geothermal hot-water supply. Adjusted hazard ratio (aHR) and 95% confidence intervals (CI) were estimated in Cox-model. Results: The aHR for all skin cancer was 1.13 (95% CI 0.79-1.63) compared with reference area. The aHR for cutaneous malignant melanoma (CMM) was 1.29 (0.77-2.16), squamous cell carcinoma (SCC) 1.03 (0.62-1.72), and BCC 1.49 (1.21-1.82). The aHR for BCC of trunk was 2.57 (1.73-3.82), and of multiple/unspecified sites 4.50 (1.57-12.94). Positive exposure-response relation was observed between the risk of BCC and the degree of volcanic/geothermal activity. Conclusion: The increase of BCC was without parallel increase of CMM or SCC indicating that exposure to ultraviolet radiation is not a confounding factor and explanation should be sought in gas emission and hot-water content previously of concern in volcanic areas.