Human 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure and thyroid cancer risk

Thyroid cancer incidence has been steadily rising since the 1970s and exposure to environmental pollutants, including persistent organic pollutants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and other dioxins, has emerged as a potential explanation for this increase. This study aimed to summarize available human studies on the association between TCDD exposure and thyroid cancer. A systematic review of the literature was performed searching the National Library of Medicine and National Institutes of Health PubMed, Embase, and Scopus databases, through January 2022, using the following keywords: "thyroid", "2,3,7,8-tetrachlorodibenzo-p-dioxin", "TCDD", "dioxin", and "Agent Orange". Six studies were included in this review. Three studies evaluated the acute exposure to the chemical factory accident in Seveso, Italy, and found a non-significant increase in the risk of thyroid cancer. Two studies investigating Agent Orange exposure among United States Vietnam War veterans found a significant risk of thyroid cancer following exposure. No association was found in one study evaluating TCDD exposure through herbicides. The current study highlights the limited information on the potential association between TCDD exposure and thyroid cancer and thus the need for future human studies, especially considering the persistent human exposure to dioxins in the environment.