OBJECTIVE: Established risk factors for endometrial cancer include age, hormone replacement therapy, and reproductive history. However, emerging evidence suggests that obesity may play a pivotal role. Most research has primarily focused on BMI, overlooking the impact of changes in obesity status over time. Therefore, our aim was to investigate whether change in obesity status is associated with increased endometrial cancer risk in young women.
METHODS: In this large-scale prospective cohort study, we used the South Korean National Health Insurance Service between 2009 and 2012. A total of 461,639 participants aged 20–39 years who completed two different health check-ups with three-year intervals and had no history of any cancer were included. Changes in obesity (BMI >25 kg/m²) were monitored over a three-year period, and participants were classified into 4 groups according to the change in obesity status (normal/normal, obese/normal, normal/obese, and persistent obese). The primary outcome was newly diagnosed endometrial cancer, and the cohort was followed up until December 2020. The Cox proportional hazards regression model was used to estimate the hazard ratios (HRs) and 95% CIs for incident endometrial cancer.
RESULTS: During 6.57 years of follow-up, 309 patients were diagnosed with endometrial cancer. The prevalence of endometrial cancer was increased with higher BMI at baseline (P for trend <0.0001). The cumulative incidence of endometrial cancer was significantly different based on the four group (log-rank test, P <0.001). Multivariable-adjusted HRs for incident endometrial cancer were 2.067 in the obese/normal group, 2.537 in the normal/obese group, and 4.123 in the persistent obese group compared with the normal/normal group.
CONCLUSIONS: We found that change in obesity status is significantly related to the risk of endometrial cancer among young women. Persistent obesity was the highest risk of endometrial cancer, and improving obesity (obesity/normal) was associated with a lower risk than becoming obesity (normal/obesity).