Further evidence for a link between silica dust and esophageal cancer

Our objective was to examine the relationship between silicosis and esophageal cancer in Hong Kong. The mortality of esophageal cancer was investigated among caisson and non-caisson workers in a cohort of 2,789 male silicotic workers in Hong Kong during the period 1981-99. The standardized mortality ratio (SMR) was calculated using the Hong Kong general population rates as reference. The indirect method proposed by Axelson was used to adjust for the confounding effects of cigarette smoking and alcohol drinking. The SMR of esophageal cancer in the entire cohort was 2.22 (95% CI 1.36-3.43, based on 20 deaths) and was 4.21 (95% CI 1.81-8.30, based on 8 deaths) in the subgroup of caisson workers who had a higher exposure to silica dust. The relative risk of esophageal cancer for caisson silicotics was reduced to 2.34 after adjusting for the effects of smoking and alcohol drinking. No more excess risk of esophageal cancer was observed among non-caisson silicotic workers after the adjustments. This historical cohort study revealed that there was an increased mortality risk of esophageal cancer among silicotics who had worked in underground caissons in Hong Kong after adjusting for cigarette smoking and alcohol drinking. We believe that the excess risk of esophageal cancer mortality among caisson workers with silicosis could best be explained by the very heavy exposure to free silica dust in their working environment.