Environmental factors and incidence of thyroid cancer in the world (1990-2019): an ecological study

Thyroid cancer (TC) is the most common endocrine malignancy. Environmental risk factors such as presence of pollutants in air as well as the combustion of fossil fuels or carbon as a cooking habit in closed environments inside houses affect thyroid hormonal homeostasis and diseases. This study aimed to estimate the association between environmental risk factors and the incidence of thyroid cancer worldwide from 1990 to 2019 including particulate pollutants coming from fossil fuels employed in closed environments. Data on the incidence of thyroid cancer and some environmental risk factors were extracted from the Global Cancer Observatory (GLOBOCAN) for 204 countries and territories from 1990 to 2019. Pearson's correlation coefficient was used to determine the correlation between the thyroid cancer incidence and environmental risk factors. Finally, a generalized additive model was fitted for modeling. R 3.5.0 was used for analysis of the data. The most relevant results showed that the age-standardized incidence rate (ASIR) of thyroid cancer has a positive and significant correlation with environmental air pollution by O₃ (r=0.63, P value<0.001), by particulate matter pollution (r=0.23, P value<0.001), and by household PM_2.5 air pollution (r=0.52, P value≤0.001). In contrast, the correlation between ASIR and high temperature (T>25.6°C) (r=-0.27, P value<0.001) is negative and significant. The modeling results showed that particulate matter pollution and O₃ pollution and household PM_2.5 air pollution which originated from solid fuels are risk factors for thyroid cancer. Therefore, more research in this field is necessary in areas with high levels of air pollution at the national and international levels.