Polyhalogenated aromatic hydrocarbon exposure mixture and risk of papillary thyroid cancer in active-duty U.S. military: A nested case-control study

Abstract

BACKGROUND AND AIM: Exposure to endocrine-disrupting chemicals has been implicated in increasing incidence of papillary thyroid cancer (PTC). The evidence of associations between PTC risk and exposure to polyhalogenated aromatic hydrocarbons (PHAHs), including polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), and organochlorine pesticides (OCPs), is largely limited to single-pollutant studies. We aimed to investigate the relationship between a PHAH exposure mixture and PTC risk. METHODS: We conducted a case-control study nested within the Department of Defense (DoD) cohort including 742 histologically-confirmed PTC cases (54% male) diagnosed 2000-2013 and 742 individually-matched controls. PHAHs were measured in pre-diagnostic sera collected 1994-2010. We used quantile g-computation to estimate the joint effect of a PHAH mixture on PTC risk, adjusting for body mass index and military service branch. Quantile g-computation is appropriate for matched case-control study design and allows the direction of weights among mixture components to vary. Our PHAH mixture included 24 lipid-corrected congeners (four PBDEs, 14 PCBs, five OCPs, and one polybrominated biphenyl). RESULTS:Mean age at PTC diagnosis was 35 (± 8) years. On average, serum samples were collected nine years before PTC diagnosis. Overall, a one-quartile increase in the PHAH mixture was non-significantly associated with 11% increase in PTC risk (95%CI=0.81-1.50). PCB-180 and PCB-118 contributed the largest total mixture weights in the positive direction, while PCB-153, PCB-187, and PBDE-100 contributed the largest total mixture weights in the inverse direction. The risk among women was elevated (OR=1.33; 95%CI=0.79-2.23), while it was relatively null among men (OR=0.90; 95%CI=0.60-1.37). CONCLUSIONS:Our study suggests that exposure to a large mixture of ubiquitous environmental pollutants is non-significantly associated with PTC risk in a young active-duty military population. However, that risk may be higher for women than men. Disclaimer: The views expressed here are the authors’ and do not necessarily reflect official policies/positions of USU, the DoD, or the CDC. KEYWORDS: Endocrine disrupting chemicals, Environmental epidemiology, Mixtures analysis