The benefit of adjuvant chemotherapy for stage I ovarian endometrioid carcinoma (OEC) remains controversial. Hence, the study sought to explore its value in stage I OEC patients.

Stage I OEC patients (1988–2018) were identified from the Surveillance, Epidemiology, and End Results (SEER) database. Multivariate Cox analysis was used to control confounders. Logistic regression was used to explore factors associated with adjuvant chemotherapy. Cox regression analysis and Kaplan-Meier curves were used to assess the survival benefits. Single-center clinical data and meta-analysis following PRISMA guidelines provided external validation.

Adjuvant chemotherapy correlated with improved survival (Hazard Ratio (HR): 0.860, p = 0.011), as did lymphadenectomy (HR: 0.842, p < 0.001). Higher age, pathological stage, and tumor grade negatively affected survival. Chemotherapy administration associated with higher pathological stage (IB: Odds Ratio (OR) 1.565, p < 0.001; IC: OR 4.091, p < 0.001), higher grade (G2: OR 2.336, p < 0.001; G3: OR 4.563, p < 0.001), and lymphadenectomy (OR 1.148, p = 0.040). Stratification analysis showed adjuvant chemotherapy failed to improve prognosis in stage IA/IB patients regardless of grade or lymphadenectomy. For stage IC patients, chemotherapy benefited grade 1-2 or grade 3 patients without lymphadenectomy, and grade 3 patients with lymphadenectomy. Meta-analysis revealed reduced recurrence in stage IC patients (OR = 0.50, p = 0.035).

Adjuvant chemotherapy confers survival benefits for stage IC patients, particularly those without lymphadenectomy.