Patterns and Predictors of Relapse Following Cytoreductive Surgery for Pseudomyxoma Peritonei

OBJECTIVE: To evaluate the incidence, timing and anatomical pattern of relapse after cytoreductive surgery (CRS) for pseudomyxoma peritonei (PMP), and identify predictors of overall and early (within 12 months) relapse. METHODS: Retrospective cohort study of consecutive patients undergoing curative-intent CRS for appendiceal PMP at a single institution (2016-2025), recording the site of first relapse. Predictors of progression-free survival (PFS) and early relapse were evaluated using Cox and logistic regression. RESULTS: Among 204 patients, CC-0/1 cytoreduction was achieved in 89% and HIPEC in 92%. At 37.1-month median follow-up, 89 patients (44%) relapsed; 3-year PFS and overall survival were 50.2% and 75.6%. Relapse was predominantly intraperitoneal, most often the pelvis and small bowel/mesentery (25% each). Histology and completeness of cytoreduction independently predicted PFS: low-grade (HR 2.18), high-grade (HR 2.79) and signet-ring PMP (HR 4.35) vs acellular mucin, CC-2/3 (HR 2.18), and male sex (HR 1.74). Early relapse occurred in 34 patients (17%), independently predicted by high-grade histology (OR 5.06) and CC-2/3 (OR 3.55). CONCLUSION: Relapse after CRS for PMP is predominantly intraperitoneal, most often the small bowel/mesentery and pelvis. Histology and completeness of cytoreduction are the principal determinants of overall and early relapse, supporting risk-stratified surveillance and selective repeat cytoreduction.