Soil selenium and oesophageal cancer incidence in China: a large ecological study of population-based cancer registry data

Incidence rates of oesophageal cancer (EC), predominantly oesophageal squamous cell carcinoma (ESCC), in areas of China are the highest worldwide. Selenium, a trace element linked to ESCC risk, likely plays a role in ESCC's enigmatic spatial distribution. We investigated the association between soil selenium and EC incidence in China. We conducted a large ecological study using 2016 population-based EC incidence data from 486 cancer registry catchments covering 380 million people and 74,000 EC cases. We assigned mean soil selenium concentrations to each area from geospatial maps. Age-standardized EC incidence rates (ASRs) were computed. We used linear regression models to estimate approximate incidence rate ratios (IRRs) for ASRs across soil selenium quintiles and for areas classified as deficient (≤ 0.2 mg/kg). The distribution of ASRs differed above and below the selenium deficiency threshold (0.2 mg/kg). Above, 100% of ASRs in females and 87% in males were < 15/100,000. Below, 81% of ASRs in females and 36% in males were < 15/100,000, with ASRs having a wide range (0 - 117.5 per 100,000 person-years). Soil selenium-deficient areas were linked to more than twofold increased EC incidence among males (IRR: 2.45; 95% CI: 2.13, 2.81) and threefold among females (IRR: 3.35; 95% CI: 2.67, 4.19). These findings support the hypothesis of selenium's role in the incidence of EC, which may arise from increased susceptibility to the carcinogenic effects of other exposures in selenium-deficient areas. In China, all EC hotspots occur in selenium deficient areas, yet there are selenium deficient areas with low EC rates.