A pooled analysis of case-control studies of thyroid cancer: cigarette smoking and consumption of alcohol, coffee, and tea

Objective: To analyze the role of smoking, alcohol, coffee and tea in relation to thyroid cancer, we conducted a pooled analysis of 14 case - control studies conducted in the United States, Europe, and Asia. Methods: The sample consisted of 2725 thyroid cancer cases ( 2247 females, 478 males) and 4776 controls ( 3699 females, 1077 males). Conditional logistic regression with strati. cation on study, age at diagnosis, and gender was used to compute odds ratios and 95% confidence intervals. Results: Thyroid cancer risk was reduced in persons who had ever smoked. The relationship was more pronounced in current smokers (OR = 0.6, 95% CI = 0.6 - 0.7) than former smokers (OR = 0.9, 95% CI = 0.8 - 1.1). There were significant trends of reduced risk with greater duration and frequency of smoking. For consumption of wine and beer, there was a significant trend of decreasing thyroid cancer risk ( p = 0.02) that was not maintained after adjustment for current smoking (p = 0.12). Thyroid cancer risk was not associated with consumption of coffee or tea. These findings were consistent in both gender-specific and histology-specific (papillary and follicular) analyses. Conclusions: Pooled analyses of these geographically diverse case - control data indicate a reduced thyroid cancer risk associated with current smoking. A reduced risk associated with alcohol was eliminated after adjustment for smoking, and caffeinated beverages did not alter thyroid cancer risk.