Occupational and socio-economic factors in the etiology of cancer of the esophagus and gastric cardia
Abstract: Adenocarcinoma of the esophagus and gastric cardia and squamous-cell carcinoma of the esophagus have a poor prognosis. The increasing incidence and the strong male predominance of esophageal and cardia adenocarcinoma are striking, and yet unexplained, patterns that should be due to unknown environmental factors. The main aim of this thesis was to study occupational and socio-economic factors in relation to these tumors. Papers I, III and IV are based on a nationwide Swedish population-based case-control study where 189 esophageal adenocarcinoma cases, 262 cardia adenocarcinoma cases, 167 esophageal squamous-cell carcinoma cases and 820 frequency-matched controls underwent personal interviews. In paper I, we investigated the role of stressful psychosocial working conditions. We found no influence of job strain, except between one job strain measure and a 2.2-fold (95% CI, 1.0-4.8) increased risk of cardia adenocarcinoma. Having a covert coping style, compared to an overt, was associated with moderately increased risks of both esophageal (OR 1.8, 95% CI, 1.2-2.8) and cardia adenocarcinoma (OR 1.5, 95% CI, 1.0-2.2). Low work pace satisfaction was associated with about 3-fold increased risks of both histological types of esophageal cancer. Thus, work-related stress does not seem to be associated with the risk of these tumors, while the interplay between a stressful work environment and the individual s responses to it may influence the risk. In paper II, we examined airborne occupational exposures among men and risk of esophageal and cardia cancers. We analyzed 12 agents in a prospective cohort study where 260 052 Swedish construction workers were followed 1971 to 2000. We found positive associations between high exposure to asbestos (IRR 4.5, 95% CI, 1.4-14.3) and cement dust (IRR 3.8, 95% CI 1.5-9.6) and risk of esophageal adenocarcinoma, and between high exposure to asphalt fumes (IRR 2.3, 95% CI, 1.0-5.3) and wood dust (IRR 4.8, 95% CI, 1.2- 19.4) and risk of cardia adenocarcinoma. No consistent associations regarding esophageal squamous-cell carcinoma were found. In paper III, the relation between socio-economic status (SES) and risk of esophageal and cardia cancers was studied. Our classification of SES was derived from each participant s occupational history. The risk of esophageal adenocarcinoma and squamous-cell carcinoma increased with decreasing SES; unskilled workers had 3.7-fold (95% CI, 1.7-7-7) and 2.1-fold (95% CI, 1.0-4.7) increased risks, respectively, compared to professionals. Adjustment for reflux, body mass and smoking attenuated the risk for esophageal adenocarcinoma, while adjustment for H. pylori infection did not influence the results. Life without a partner was associated with over 2-fold increased risks of esophageal adenocarcinoma and squamous-cell carcinoma, associations remaining after multiple adjustments. Thus, both histological types of esophageal cancer are linked to low SES and single life, associations only partly explained by known risk factors. Finally, in paper IV, we investigated specific airborne occupational exposures in relation to risk of esophageal and cardia cancers. Based on each participant s occupational history we assessed cumulative airborne exposure for 10 agents, analyzed individually and combined. Further, occupations and industries were analyzed. Tendencies of positive associations between high exposure to pesticides and risk of esophageal (OR 2.3, 95% CI, 0.9-5.7) and cardia adenocarcinoma (OR 2.1, 95% CI, 1.0-4.6) were found. Workers highly exposed to combined particular agents were at a seemingly increased risk of esophageal squamous-cell carcinoma (OR 1.7, 95% CI, 1.0-2.9). There were no other consistent associations. Thus, airborne occupational exposures do not seem to be of major importance in the etiology of esophageal or cardia adenocarcinoma.
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