Background: Peritoneal metastases (PM) are a well-known poor prognostic factor. The aim of this study was to investigate the factors affecting recurrence and prognosis after R0 resection for colorectal cancer with synchronous peritoneal metastases. Methods: We conducted a multi-institutional retrospective analysis of 72 patients without distant metastases who underwent R0 surgery between 1991 and 2007 for colorectal cancer with PM localized to the adjacent peritoneum. Clinicopathological variables were analyzed for their significance to recurrence and prognosis. Results: Recurrence was found in 51 patients (70.8 %) after R0 surgery. In logistic regression analyses, lymph node metastasis was shown to be an independent factor affecting recurrence. Non-intensive or no postoperative chemotherapy and eight or fewer dissected lymph nodes were identified as independent poor prognostic factors using the Cox proportional hazards model. Among patients who received postoperative chemotherapy, prognosis was significantly better in those who received intensive adjuvant chemotherapy using camptothecin-11 or oxaliplatin after R0 surgery than in those who received non-intensive chemotherapy. Among 47 patients whose recurrence date was known, 33 patients (70.2 %) experienced recurrence within 18 months after R0 surgery for peritoneal metastases, and hematogenous recurrence was observed significantly more often than peritoneal recurrence. Conclusions: Harvesting of more than eight lymph nodes and administration of intense adjuvant chemotherapy after R0 surgery are recommended for greater prediction accuracy and improved prognosis. Intensive follow-up should be performed within 18 months after R0 surgery for colorectal cancer with synchronous peritoneal metastases.
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