Trends in the management and prognosis of mucinous borderline ovarian tumors: analysis of 12,766 cases from the JSOG Gynecologic Tumor Registry (2004-2018).

Background: Mucinous borderline ovarian tumors (MBOTs) are rare neoplasms with excellent prognosis, yet the optimal surgical extent remains controversial. No large-scale study in Japan has evaluated treatment trends and prognostic factors for MBOTs. This study aimed to clarify their clinicopathological features, management patterns, and survival outcomes using a nationwide registry.

Methods: Data were obtained from the Japan Society of Obstetrics and Gynecology Gynecologic Tumor Registry, including 96,476 ovarian tumors treated between 2004 and 2018. Among them, 12,766 MBOT cases were identified. Surgical procedures-hysterectomy, omentectomy, lymphadenectomy, and adjuvant chemotherapy-were analyzed. Survival analyses of 8564 cases with complete prognostic data were performed using Kaplan-Meier and Cox proportional hazards models.

Results: Over 90% of MBOTs were stage I, and the median age was 52 years. Hysterectomy was performed in 50.8%, omentectomy in 57.9% (2015-2018 subset), and lymphadenectomy in 7.6%. Only 2.6% received adjuvant chemotherapy. The 5-year overall survival exceeded 95%. Multivariate analysis identified age ≥ 50 years (HR 2.5, 95% CI 1.8-3.6) and stage IC (HR 2.7, 95% CI 1.9-3.6) as independent adverse factors. Omentectomy showed a marginal survival benefit (HR 0.6, p = 0.05), whereas hysterectomy, lymphadenectomy, and chemotherapy conferred no advantage. Chemotherapy correlated with poorer outcomes, likely due to confounding by indication.

Conclusions: This nationwide cohort-the largest MBOT series reported to date-demonstrates conservative management with excellent prognosis in Japan. Radical surgery and chemotherapy provide no survival benefit, whereas fertility-sparing surgery appears appropriate for younger patients.