Longer lifetime exposure to female hormones may increase the risk of thyroid cancer in women, according to research presented on June 14 at ENDO 2026, the Endocrine Society's annual meeting in Chicago, Illinois. The study suggests that reproductive and hormonal factors could play a role in the development of thyroid cancer.
Thyroid cancer is more common among women than men, but the reasons for this difference have not been fully understood. Scientists from the College of Medicine at The Catholic University of Korea in Seoul designed a nationwide population-based study involving approximately 5.7 million women aged 40 years or older. They used data from the Korean National Health Insurance Service, which provides universal health coverage.
The participants had taken part in breast and cervical cancer screening programs between 2010 and 2011 and provided reproductive health information through standardized questionnaires. Researchers followed these women until they were diagnosed with thyroid cancer, died, or reached the end of follow-up in 2023. The associations between reproductive factors and incidence of thyroid cancer were analyzed using Cox proportional hazards regression models. These models were adjusted for age, smoking status, alcohol consumption, regular physical activity, body mass index, hypertension, diabetes, dyslipidemia, history of cancer, and household income levels.
The findings showed that about 2.4 out of every 1,000 people per year developed thyroid cancer during the study period. A longer reproductive span was linked to a progressively higher risk of developing thyroid cancer. Additionally, use of hormone replacement therapy was associated with an increased risk—especially among those who received hormone replacement therapy for five years or more.
