Examining the relationship between cesarean section scar and endometrial cancer

Objective: The incidence of endometrial cancer (EC) has been increasing annually. Studies have reported that cesarean section (CS) is associated with a higher risk of developing EC than vaginal delivery (VD). However, few studies have examined the relationship between CS and EC development.
Methods: Data were extracted from the medical records of patients with EC and a history of childbirth who underwent EC treatment at 3 institutions. Factors contributing to EC development were analyzed between April 2010 and December 2024.
Results: Among patients EC and a history of childbirth, 8.7% (69/794) had undergone CS, and 50.7% (35/69) developed a CS scar. Compared with patients who had a VD or those without a CS scar, patients with a CS scar showed significantly shorter intervals from delivery to EC onset (VD: p=0.013; non-CS scar: p=0.031). A narrower residual myometrial thickness/adjacent myometrial thickness (RMT/AMT) ratio of the CS scar was significantly associated with a shorter interval from the last delivery to EC onset (p=0.034) and was independently associated with earlier EC onset after the last delivery in both univariate and multivariate analyses (p<0.001 and p=0.030, respectively).
Conclusion: A narrower RMT/AMT ratio in the CS scar was considerably associated with a shorter interval from the last delivery to EC onset.