Toluene concentrations in the blood and risk of thyroid cancer from National Industrial Complexes: a population-based cohort study

Abstract

Background/AimAlthough monocyclic aromatic hydrocarbons are classified as definite or possible carcinogen, studies on toluene with thyroid cancer risk are limited. This study was conducted to examine potential associations between blood toluene and the incidence risk of thyroid cancer, and the effect modification of living environment among residents living near industrial complex.MethodsWe conducted a prospective cohort study using data from the Industrial Monitoring Project of South Korea. Study participants in living near National Industrial Complexes were recruited from January 2003 to 2010. Incidence and mortality cases of thyroid cancer (C73, ICD-10 code) was identified through National Cancer Registry and Statistics Korea, respectively. Blood toluene was measured by gas chromatography mass spectrometry. We used Cox proportional hazards regression models to estimate incidence rate ratios (IRRs) and 95% confidence intervals (CI) between blood toluene and thyroid cancer risk.ResultsThe geometric means of the toluene concentration in blood were 0.62 μg/L for cases and 0.29 μg/L for noncases. During the follow-up (median 8.7 years), 32 incident cases of thyroid cancer were diagnosed. After adjusting for potential confounders, a positive association between blood toluene and thyroid cancer was found (IRR=3.38, 95% CI = 1.12-10.24 in the highest tertile vs. the lowest tertile, p-value=0.03). This positive association was stronger in people living near a road (≤50 meters) (IRR= 5.14, 95% CI = 1.12-23.67 in the highest tertile vs. the lowest tertile, p-value=0.04).ConclusionsBlood toluene may be positively associated with the incidence risk of thyroid cancer. Moreover, this association of blood toluene with thyroid cancer risk may also be stronger in people living near a road.