Elevated Risk of Thyroid Malignancy in Biological Males Taking Estrogen Hormone Therapy.

Biologically male patients prescribed estrogen hormone therapy had a 2.35-fold higher risk of thyroid malignancy within 5 years compared to those not taking estrogen.

• The estrogen treatment cohort had a 0.64% risk for diagnosis of thyroid malignancy within 5 years
• The comparison cohort not taking estrogen had a 0.27% risk
• Relative risk: 2.35, 95% confidence interval: 1.34-4.15, P = .002
• Cohorts were balanced for demographic factors as well as known risk factors for thyroid malignancy

The study identified 6394 biologically male patients prescribed estrogen hormone treatment across 65 healthcare organizations.

• Data were drawn from the TriNetX Research Network
• The average age of patients was 44.4 years
• Patients were required to have at least 5 years of follow-up
• This was a retrospective cohort study design

This study represents the first identified association between estrogen therapy and thyroid malignancy in biologically male patients.

• Prior epidemiological studies have shown exogenous estrogen is associated with increased thyroid malignancy risk in females
• No prior studies had investigated this association among biological males undergoing estrogen hormone therapy
• The role of estrogen in developing thyroid malignancy is described as 'poorly understood'