Introduction/Background*The prognostic value of endometriosis in ovarian clear cell carcinoma (OCCC) remains to date a field of contention. The aim of this study was to ascertain whether endometriosis is associated with improved survival outcomes in OCCC.

Methodology MEDLINE, Scopus and Cochrane Database were searched for relevant references from inception until May 2021 in line with PRISMA guidelines. Observational studies (OSs) assessing the prevalence and prognostic impact of endometriosis in OCCC were included. The methodologic index for non-randomised studies was used to evaluate the quality of the included studies. We pooled proportions to calculate the prevalence of endometriosis, whilst dichotomous variables were assessed using hazard ratio (HR). Confidence intervals were set at 95%. Heterogeneity was assessed using Cochran’s Q test, with an I² > 50% and p-value <0.1 denoting significant inter-study heterogeneity. Statistical analysis was performed using the RevMan software version 5.3 and MedCalc. The level of statistical significance was set at p-value < 0.05.

Twenty-one OSs were included The studies were of moderate quality and characterised by significant clinical heterogeneity. Pooled analysis rendered a summary proportion of 43.56% [(95% CI 37.53% - 49.68%); I²=90.21%] for the outcome of endometriosis prevalence. Pooled results from 11 studies demonstrated no significant impact of endometriosis on progression-free survival (PFS) [HR=0.95, (95% CI 0.73 - 1.23), p-value=0.69; I²=56%]. Conversely, pooled results from 19 studies showed that endometriosis was significantly associated with improved overall survival (OS) [HR=0.82 (95% CI 0.73 - 0.92), p-value=0.001; I²=45%].

Conclusion*Approximately 50% of OCCC cases were developed on the background of endometriosis. Our results demonstrated that endometriosis conferred an improved OS in women with OCCC. Larger future studies are warranted to further elucidate the intrinsic relationship between endometriosis and OCCC.