Recurrence and Malignant Transformation After Borderline Ovarian Tumors: A Systematic Review and Meta-analysis

Borderline ovarian tumours (BOTs) frequently affect women of reproductive age. Fertility-sparing surgery (FSS) is commonly offered, but recurrence risk varies by surgical approach and histological subtype, while malignant transformation remains incompletely defined. This systematic review and meta-analysis aimed to quantify recurrence and malignant transformation risks following different surgical strategies for BOTs.

A prospectively registered protocol (PROSPERO: CRD420251172155) was followed. Studies of adult women with histologically confirmed BOTs undergoing FSS - unilateral or bilateral cystectomy, unilateral salpingo-oophorectomy (USO), or USO with contralateral cystectomy - or radical surgical staging (pelvic clearance) were included. Random-effects meta-analyses generated pooled risk estimates with 95% confidence intervals (CIs); heterogeneity was assessed using I². Methodological quality was evaluated using MINORS.

Forty-one studies including 5,364 women were analyzed, with follow-up ranging from 7 months to 15 years. Recurrence following FSS was highest after cystectomy-based procedures: 0.31 (95%CI=0.15-0.47; I²=97.24%) after unilateral cystectomy and 0.41 (0.26-0.57; I²=80.59%) after bilateral cystectomy. Lower recurrence was observed after USO (0.13; 0.10-0.16; I²=81.55%) and USO with contralateral cystectomy (0.31; 0.17-0.45; I²=91.40%). Radical surgery was associated with the lowest recurrence risk (0.03; 0.02-0.04; I²=26.42%). In serous BOTs, recurrence after cystectomy was 0.29 (0.23-0.56) and after USO 0.15 (0.09-0.24). In mucinous BOTs, corresponding estimates were 0.26 (0.14-0.38) and 0.08 (0.02-0.13). Overall malignant transformation occurred in 1% of women (0.01; 0.01-0.02) but increased substantially following recurrence (0.22).

Cystectomy-based FSS is associated with significantly higher recurrence than oophorectomy-based approaches or radical surgery. Although malignant transformation is rare overall, its marked increase following recurrence highlights the need for histology-informed counselling and long-term, risk-adapted surveillance.