Background/Aims: Peritoneal metastasis (PM) is a well-known predictor of poor prognosis. This study aims at identifying factors affecting recurrence and prognosis after R0 resection for colorectal cancer (CRC) with synchronous PM. Methods: A multi-institutional, retrospective analysis of 172 patients with R0 surgery for CRC with PM was conducted. Clinicopathological variables were analyzed for their significance in contributing toward recurrence and prognosis. Results: Lymph node (LN) metastasis was an independent factor affecting recurrence as indicated by logistic regression analyses. The following factors were independent predictors of poor prognostic using the Cox proportional hazard model: LN metastasis, no postoperative adjuvant chemotherapy, five or fewer dissected LNs, and preoperative high serum carbohydrate antigen 19-9 levels. Of the patients undergoing postoperative adjuvant chemotherapy, no significant differences were observed in recurrence rate and disease-free interval between those with intensive adjuvant chemotherapy and those with non-intensive chemotherapy. After R0 surgery for PM, 90 patients (76.3%) experienced recurrence by 18 months, and hematogenous recurrence occurred significantly more often than peritoneal recurrence. Conclusion: Harvesting of more than 5 LNs and administration of postoperative adjuvant chemotherapy after R0 surgery are recommended for prognosis improvement. Intensive follow-up should be performed within 18 months after R0 surgery for CRC with synchronous PM.
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