Occupational and Environmental Determinants for Benign Thyroid Disease and Follicular Thyroid Cancer

Occupational and environmental determinants of benign thyroid disease and follicular thyroid cancer were evaluated in a series of cases in 1977-1987. Of the cases initially diagnosed as follicular thyroid cancer, only 31 remained after a reclassification, whereas 44 were found to be benign thyroid disease. Both series were compared with 387 randomly selected population controls. Occupational solvent exposure was strongly associated with benign thyroid disease (odds ratio, OR, 2.8; 95% confidence interval, 95% CI, 0.9-9.0 for women and OR 18.9; 95% CI 2.2-161 for men). Eight of the nine men found to have benign disease had been exposed to solvents, and six of them to trichloroethylene. For both types of cases, a private well at the birth address increased the risk, OR 2.0; 95% CI 0.9-4.0 and OR 3.0; 95% CI 1.2-7.2, respectively, whereas the risk was lower for those living in coastal areas. Less fish and shellfish in the diet increased the risk for malignant thyroid disease only. Although based on small numbers, the study indicates etiologic roles of occupational and environmental factors for both conditions studied. The influences of occupation and diet differ, however, for the two outcomes.