Abstract
Thyroid cancer is the most common type of endocrine cancer diagnosed in the U.S. and prognosis is highly dependent on the histologic type. Firefighters experience a higher risk of thyroid cancer than non-firefighters and higher exposure to endocrine disrupting chemicals (EDCs) implicated in thyroid disorders. This dissertation examines the histologic types of thyroid cancer, and the association of occupational risk factors and thyroid disorders among firefighters. We utilized data from the Florida Cancer Data System (FCDS) linked with data from the Fire Marshalls Office (FMO) to examine the distribution of thyroid cancer histologic types categorized into papillary, follicular, and rare/aggressive types among firefighters (n=120) compared to white-collar (n=4,858), blue-collar (n=651), service (n=825), and other occupational groups (n=1,774) diagnosed with thyroid cancer in Florida in years 1981-2014. We also examined the age and tumor stage at diagnosis. We employed data from the Florida Firefighter Cancer Initiative (FCI) Polybrominated Diphenyl Ether (PBDE) and Thyroid Function Study (n=278) to determine the prevalence and predictors of thyroid disorder and to explore the moderating effect of family history on the association of occupational risk on thyroid dysfunction. The distribution of the histologic types of thyroid cancer was different in firefighters compared to service, white-collar, blue-collar, and other occupational groups. Thyroid peroxidase antibody (TPOAb) was high among participating firefighters but there was no significant association with the limited occupational risk factors studied. Thyroid antibodies also strongly predicted serum thyroid stimulating hormone (TSH) concentration. TPOAb is associated with worse outcomes for certain cancers and cardiovascular diseases and may increase the risk of thyroid cancer. These findings highlight the need for more studies examining thyroid dysfunction and chronic disease association among firefighters.