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Background: The greater omentum is routinely resected during cytoreductive surgery (CRS), but few studies have analyzed the rationale behind this. This study aimed to assess the prevalence of omental metastases (OM) and the correlation between macroscopically suspected and microscopically confirmed OM, in patients with pseudomyxoma peritonei (PMP) or colorectal peritoneal metastases (PM)., Method: All patients without previous omentectomy, treated with initial CRS and hyperthermic intraperitoneal chemotherapy for PMP or colorectal PM, at Uppsala University Hospital in 2013-2021, were included. Macroscopic OM in surgical reports was compared with histopathological analyses., Results: In all, 276 patients were included. In those with PMP, 112 (98%) underwent omentectomy and 67 (59%) had macroscopic suspicion of OM. In 5 (4%) patients, the surgeon was uncertain. Histopathology confirmed OM in 81 (72%). In patients with macroscopic suspicion, 96% had confirmed OM (positive predictive value, PPV). In patients with no suspicion, 24% had occult OM (negative predictive value, NPV = 76%). In patients with colorectal PM, 156 (96%) underwent omentectomy and 97 (60%) had macroscopic suspicion. For 5 (3%) patients, the surgeon was uncertain. OM was microscopically confirmed in 90 (58%). PPV was 85% and NPV was 89%. The presence of OM was a univariate risk factor for death in PMP (HR 3.62, 95%CI 1.08-12.1) and colorectal PM (HR 1.67, 95%CI 1.07-2.60), but not in multivariate analyses., Conclusion: OM was common and there was a high risk of missing occult OM in both PMP and colorectal PM. These results support the practice of routine omentectomy during CRS.

Background: Selecting colorectal patients for HIPEC-surgery needs improvement. The study aim was to improve the colorectal peritoneal score (COREP) and to compare it with three other scores: peritoneal-surface disease-severity score (PSDS), colorectal-peritoneal metastases prognostic-surgical-score (COMPASS), and the CEA/PCI ratio., Method: Twelve preoperative factors were chosen to evaluate for COREP score modification. Criteria from logistical analyses were set to qualify for the modified COREP score (mCOREP). Odds ratios were used to assign score points for the eligible factors with open/close laparotomy prediction as endpoint. mCOREP was applied internally and compared with the original COREP, PSDS, COMPASS, and CEA/PCI ratio. Odds ratios, hazard ratios, and Kaplan-Meier curves were used for comparison., Results: Seven factors qualified for mCOREP: CEA, CA 19-9, CA-125, C-reactive protein, albumin, platelet count and signet-cell histology. mCOREP was superior to the original COREP. mCOREP and COMPASS scores were the only scores with independent prognostic value. The mCOREP had the best discriminatory ability between its prognostic groupings. mCOREP 11 + had 9 months survival with half of patients being open/close surgery., Conclusion: The mCOREP has successfully been simplified while still improving its prognostic ability. The mCOREP and COMPASS scores have independent prognostic value. Patients with mCOREP 11 + may not benefit from treatment.