Impact of Changes in Obesity and Abdominal Obesity on Endometrial Cancer Risk in Young Korean Women: A Nationwide Cohort Study.

Background: The rising incidence of endometrial cancer in young women parallels the increasing prevalence of obesity, a well-established risk factor. However, the impact of longitudinal changes in obesity and abdominal obesity on early-onset endometrial cancer remains insufficiently understood.

Methods: This nationwide cohort study utilized data from the Korean National Health Insurance Service. Women aged 20-39 years who underwent two health examinations at a three-year interval between 2009 and 2015, with no history of cancer, were included. Participants were categorized based on changes in obesity (BMI ≥25 kg/m²) or abdominal obesity (waist circumference ≥85 cm) into four groups: stable non-obese, non-obese to obese, obese to non-obese, and stable obese. The risk of endometrial cancer was assessed using Cox proportional hazards models.

Results: Among 935,600 women, 798 developed endometrial cancer. Compared to the stable non-obese group, adjusted hazard ratios (HRs) for endometrial cancer were 1.940 (1.468-2.563), 2.083 (1.447-3.001), and 2.083 (1.447-3.001) in the non-obese to obese, obese to non-obese, and stable obese groups, respectively. Regarding abdominal obesity, the adjusted HRs were 2.048 (1.581-2.651), 2.302 (1.684-3.146), and 4.394 (3.557-5.427), respectively. The risk of cancer was higher in the obese to non-obese group than in the non-obese to obese group.

Conclusion: Changes in obesity and abdominal obesity status were associated with early-onset endometrial cancer, with persistent abdominal obesity showing the highest risk.

Impact: These findings support the need for early, sustained obesity interventions to reduce endometrial cancer risk in young women.