Smoking as a Potential Risk Factor for Thyroid Cancer in Patients With Thyroid Nodules

Background Smoking is a known carcinogen and its relationship with the development of thyroid cancer (TC) is not well established and prior evidence shows a possible protective relationship. We aim to evaluate the impact of smoking on the development of TC. Methods This is a retrospective cohort study of adult patients who were diagnosed with a thyroid nodule(s) between 2005 and 2025. Cohorts were developed based on smoking status. Patients with the diagnosis of multiple endocrine neoplasia syndrome or who had known TC were excluded. Propensity score matching (PSM) was performed. The primary outcome was diagnosis of TC. Hazard ratios (HRs) and 95% confidence intervals were calculated. Cohorts were then divided into subgroups based on sex and racial groups with the same analysis. Results There were 404,811 individuals identified who were smokers and had thyroid nodules. Average age was 60 +/− 15 years, with 69% of the cohort being female and 70% white. TC developed in 3.4% of smokers with nodules compared to 1.2% of nonsmokers (HR = 2.60). Subgroup analysis revealed an increased risk across all sex and racial groups. Female smokers had a HR than males at 2.62. Across racial groups, Black patients had the highest HR at 2.91. All groups had confidence intervals that did not cross one. Discussion In this retrospective cohort study, smoking was significantly associated with an increased risk of developing TC. There was an increased risk of developing TC in all groups, and Black patients had the highest HR highlighting an area that warrants further investigation.