#1428 Impact of cytoreductive surgery outcomes in primary mucinous ovarian cancer – retrospective multicentre international study

Introduction/Background Mucinous ovarian cancer (MOC) represents 3% of ovarian cancers. While early-stage disease has excellent outcomes (>80% 5-year survival), advanced disease outcomes are poor (17% 5-year survival, median 12-36 months). Evidence surrounding the impact of cytoreductive surgery (CRS) has been driven predominantly by high-grade serous cancers, with sparse data specific to chemotherapy-resistant MOC. This study assesses the impact of surgical cytoreduction on survival outcomes in mucinous ovarian cancer.

Methodology International retrospective multicentre cohort study from the UK and The Netherlands of MOC patients diagnosed between January 2005-December 2023. Survival was assessed using Cox proportional hazards models and Kaplan-Meier analysis.

Results Of 724 patients, 627 (87%) were FIGO stage I; Of 90 patients with stage II-IV disease, 62 (69%) achieved complete cytoreduction (CCR), 16 (18%%) had <1cm residual disease (MRD), and 12 (13%) had >1cm MRD. In patients with FIGO stage II-IV patients, 24-month overall survival was 60%, 27% and 15% in those who achieved CCR, <1cm MRD, >1cm MRD respectively. The risk of death was increased (HR 3.22, 95% CI 1.76-5.88) in women with any residual disease when compared to those who achieved CCR. When comparing the risk of death in women with >1cm MRD and <1cm MRD, the hazard ratio was 2.14 (95% CI 0.9-5.05).

Conclusion This represents one of the largest confirmed MOC cohorts reported to date. We have been able to demonstrate that residual disease is a highly significant poor prognostic indicator in MOC, increasing death risk threefold. These findings represent the impact of residual disease without stratification by invasion subtype. Complete cytoreduction is associated with better OS with limited survival difference between optimal (<1cm) and suboptimal (>1cm) cytoreduction in this large dataset of patients. Complete cytoreduction through meticulous intra-operative and peri-operative surgical planning in this chemotherapy-resistant disease should be the goal of care.