Validation and Clinical Use of the Japanese Classification of Colorectal Carcinomatosis: Benefit of Surgical Cytoreduction Even without Hyperthermic Intraperitoneal Chemotherapy

Background: This study aimed to validate an easy to use practical classification of peritoneal metastasis arising from colorectal cancer. Patients and Methods: Data from 2,134 consecutive patients who underwent resection for colorectal cancer at a single institution were reviewed. Peritoneal metastasis was classified depending on extent into three groups (P1–P3). The macroscopic radical resection rates and survival of patients with colorectal cancer complicated with peritoneal metastasis were analyzed. Results: Of the 2,134 patients, 116 (5.4%) had peritoneal metastasis. Among them, 20 (17.2%) underwent macroscopic radical resection. Tumor location on the right side was associated with more extensive peritoneal metastasis (p = 0.010). Male gender (p = 0.0027), liver metastasis (p = 0.0021), and P3 peritoneal metastasis were independent risk factors for noncurative resection. The Cox proportional hazards model showed that gender (p = 0.031), operation period (p = 0.031), and macroscopic radical resection for colorectal cancer and peritoneal metastasis (p = 0.031) were independent prognostic factors. Conclusions: Being female with left colon cancer complicated with P1 or P2 peritoneal metastasis is a good indicator for macroscopic radical resection if liver metastasis is absent. The present classification helped to determine surgical indication for patients with colorectal cancer complicated with synchronous peritoneal metastasis in routine clinical practice.