Objective: Little is known about the role of estrogen in thyroid cancer development. We aimed to evaluate the association between hysterectomy or bilateral salpingo-oophorectomy (BSO) and the risk of subsequent thyroid cancer.
Design: A nationwide cohort study.
Methods: Data from the Korea National Health Insurance Service between 2002 and 2017 were used. A total of 78 961 and 592 330 women were included in the surgery group and no surgery group, respectively. The surgery group was categorized into two groups according to the extent of surgery: hysterectomy with ovarian conservation (hysterectomy-only) and BSO with or without hysterectomy (BSO).
Results: During 8 086 396.4 person-years of follow-up, 12 959 women developed thyroid cancer. Women in the hysterectomy-only (adjusted hazard ratio = 1.7, P < 0.001) and BSO (adjusted hazard ratio = 1.4, P < 0.001) groups had increased risk of thyroid cancer compared to those in the no surgery group. In premenopausal women, hysterectomy-only (adjusted hazard ratio = 1.7, P < 0.001) or BSO (adjusted hazard ratio = 1.4, P < 0.001) increased the risk of subsequent thyroid cancer, irrespective of hormone therapy, whereas, there was no significant association between hysterectomy-only (P = 0.204) or BSO (P = 0.857) and thyroid cancer development in postmenopausal women who had undergone hormone therapy.
Conclusions: Our findings do not support the hypotheses that sudden or early gradual decline in estrogen levels is a protective factor in the development of thyroid cancer, or that exogenous estrogen is a risk factor for thyroid cancer.