Relationship between uterine fibroids and risk of cancers: Population‐based retrospective cohort study

Objective Numerous studies have assessed the relationship between estrogen and cancer, and an association between uterine fibroids and an increased risk of endometrial cancer and thyroid cancer has been found. However, previous studies are limited by small sample sizes and lack of information on patient characteristics. This population‐based retrospective cohort study aimed to confirm the association between uterine fibroids and cancer risk. Methods This population‐based retrospective cohort study used insurance information recorded in the Korea's Health Insurance Review and Assessment Service from January 1, 2009, to December 31, 2020. Patients with a diagnosis of uterine fibroids and uterine fibroid removal surgery code were included in the uterine fibroid group. Women who visited a clinic for a health checkup were included in the non‐uterine fibroid group. Results In total, 714 171 individuals were studied, 492 610 in the non‐uterine fibroids group and 221 561 in the uterine fibroids group. The all‐site cancer hazard ratio (HR) of the uterine fibroid group was higher than that of the non‐uterine fibroid group (all sites: HR, 1.399, confidence interval [CI]: 1.346–1.454), with HR for breast 1.263 (CI: 1.177–1.354), uterus 2.459 (CI: 2.009–3.010), ovary 1.349 (CI: 1.097–1.659), kidney 1.432 (CI: 1.014–2.022), thyroid 1.693 (CI: 1.591–1.800), and retroperitoneum and peritoneum 3.059 (CI: 1.263–7.414). Conclusion Surgically treated uterine fibroids are associated with increased cancer risk. They are associated with an increased risk of breast, uterine, ovarian, kidney, thyroid, peritoneal, and retroperitoneal cancers.