Longer hormone exposure may increase thyroid cancer risk in women

Longer lifetime exposure to female hormones may increase the risk of thyroid cancer in women, according to a study being presented Saturday at ENDO 2026, the Endocrine Society's annual meeting in Chicago, Ill. The research suggests reproductive and hormonal factors may be involved in thyroid carcinogenesis.

Thyroid cancer occurs more frequently in women than in men, but the reasons for the increase remained unknown. Scientists from the College of Medicine at The Catholic University of Korea in Seoul designed research to find out why. They conducted a nationwide population-based study of approximately 5.7 million women aged 40 years or older, using data from the Korean National Health Insurance Service, the program that provides universal health coverage.

The study population had participated in breast and cervical cancer screening programs between 2010 and 2011, where they shared reproductive health details using standardized questionnaires. The women were followed until the diagnosis of thyroid cancer, death or the end of follow-up in 2023. Associations between reproductive factors and the incidence of thyroid cancer were evaluated using Cox proportional hazards regression models. Multivariable 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 scientists found that about 2.4 out of every 1,000 people per year develop thyroid cancer. A longer reproductive span was associated with a progressively increased risk of thyroid cancer. Use of hormone replacement therapy (HRT) was also associated with an increased risk of thyroid cancer, with a stronger association observed among women who received HRT for five years or more.

These results show how common life events in women, such as the timing of menopause and use of hormone therapy, may influence cancer risk. A woman's reproductive history could be considered in assessing her individual risk to developing thyroid cancer."

Jinyoung Kim, M.D. Ph.D., Assistant Professor, College of Medicine, The Catholic University of Korea