Advancing Education, Research, and Quality of Care for the Head and Neck oncology patient.
Importance: Estrogen may play a role in the development of thyroid cancer given the increased prevalence amongst females, specifically those of reproductive age. Previous studies have been inconclusive on the role oral contraceptives play in the development of thyroid cancer.
Objective: To determine if exogenous estrogen use is associated with thyroid cancer development.
Design, Setting, Participants: The TriNetX Network was queried to retrospectively identify female patients with and without exogenous estrogen exposure between 2008 and 2018. Cohort 1 contained women between the ages of 18-45 that had used combined oral contraceptives, cohort 2 contained the same age group who had not used contraceptives containing estrogen. The third cohort contained women over the age of 50 who had used hormone replacement therapy and the fourth contained women of the same age that had not. The incidence of thyroid cancer was compared between women who had exogenous estrogen and those who had not amongst the same the age demographics. The cohorts propensity-matched for age, race/ethnicity, disorders of the thyroid, and radiation exposure.
Main Outcome(s) and Measure(s): The risk for thyroid malignancy incidence (ICD-10 CM C73) after five years was compared between female patients who had used exogenous estrogen and a propensity score-matched control group who had not
Results: In total, 821,595 patients were identified as having taken used combined oral contraceptives containing ethinyl estradiol between 2008 and 2018 and 3,592,339 had not. After matching, 722,566 patients were in each cohort. In comparison to the control group, those with OC intake had a lower risk of a thyroid cancer diagnosis (RR, 0.69; 95% CI, 0.65-0.722). Additionally, 709,699 patients were identified to be taking hormone replacement therapy in this time range and 7,595,530 patients in this age group had not been. In this comparison, no significant difference was found with the incidence of thyroid cancer development (RR, 1.034; 95% CI, 0.995-1.074).
Conclusions and Relevance: Combined oral contraceptives may have a negative association with the development of thyroid cancer. Additionally, no significant difference in the risk of thyroid cancer was identified in post-menopausal women using hormone replacement therapy. Additional research should include information on the factors that may impact estrogen in the body in order to more accurately determine the association between exogenous estrogen exposure and thyroid cancer development.