![Sample our Medicine, Dentistry, Nursing & Allied Health journals, sign in here to start your FREE access for 14 days]({"type":"image" , "src" : "/sda/5944/TOC-Subject-Sample-2021-Medicine-Dentistry-Nursing-Allied-Health.jpg"})
Abstract
English language case–control studies reporting on the association of thyroid cancer occurrence with smoking and alcohol drinking are summarized. Two independent researchers performed study selection and data extraction. Random effects model was applied and external adjustment was performed to control for important confounders. Twenty reports published between 1987 and 2007 were included in quantitative synthesis. For smoking, mean association was inverse (odds ratio [OR]: 0.785; 95% CI: 0.701–0.879) remaining after adjustment for alcohol drinking; heterogeneity was moderate. For alcohol drinking, mean association was inverse (OR: 0.795; 95% CI: 0.660–0.958) (remaining after adjustment for smoking, OR: 0.832; 95% CI: 0.688–1.007); heterogeneity was large becoming moderate after adjustment. Data from case–control studies identified showed inverse mean association between thyroid cancer occurrence and ever-smoking or ever-drinking alcohol.
Acknowledgements
The author wishes to express his gratitude to all the investigators/authors of individual studies included in this present analysis for their kindness to respond to requests for support of this work by providing the author with any data or information available. Also, the author expresses his special thanks to Dimitris Liakos and George Stefanakos for working on this project by providing their independent assessment for selection of eligible reports as well as for data extraction.
Financial & competing interests disclosure
The author has no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.
No writing assistance was utilized in the production of this manuscript.
Key issues
• Previous published data concluded on inverse association existing between thyroid cancer occurrence and smoking or alcohol drinking.
• Pooled analysis of individual patient data published in 2003 made it possible adjusting for confounding factors; yet, reports of studies published in the international literature might not provide for direct adjustment given lack of or incomplete reporting of detailed quantitative data for risk stratification factors for cases and controls.
• In the present analysis, quantitative synthesis of published reports was attempted by applying external adjustment to control for important confounders to overcome lack or limited reporting of risk stratification factors.
• Unadjusted estimates show inverse mean association of ‘ever smoking’ or ‘ever drinking alcohol’ with occurrence of thyroid cancer compared with ‘never-exposed’ status, which remained inverse after external adjustment for alcohol drinking and for smoking, respectively.
• Estimates obtained after external adjustment show that association of ‘ever-exposed’ status with occurrence of thyroid cancer seems to remain inverse across various levels of exposure prevalence and wide range of association estimates considered between alcohol or smoking and occurrence of thyroid cancer (perhaps, except when such an inverse association of smoking with thyroid cancer occurrence becomes stronger).
• Neither were other potential confounders or effect modifiers considered nor adjusted for in the analysis thus, future studies would be designed in a way that important information for confounder factors or effect modifiers can be captured and analyzed.
• True between-study dispersion of effect size crosses the null value of 1.0 suggesting that future studies of that kind may show even positive association.