Objectives To assess the associations between occupational exposure to biocides and pesticides and risk of thyroid cancer.

Methods Using data from a population-based case–control study involving 462 incident thyroid cancer cases and 498 controls in Connecticut collected in 2010–2011, we examined the association with occupational exposure to biocides and pesticides through a job-exposure matrix. We used unconditional logistic regression models to estimate OR and 95% CI, adjusting for potential confounders.

Results Individuals who were occupationally ever exposed to biocides had an increased risk of thyroid cancer (OR=1.65, 95% CI 1.16 to 2.35), and the highest risk was observed for the high cumulative probability of exposure (OR=2.18, 95% CI 1.28 to 3.73). The observed associations were similar when we restricted to papillary thyroid cancer and well-differentiated thyroid cancer. Stronger associations were observed for thyroid microcarcinomas (tumour size ≤1 cm). No significant association was observed for occupational exposure to pesticides.

Conclusions Our study provides the first evidence linking occupational exposure to biocides and risk of thyroid cancer. The results warrant further investigation.