Clinical benefit of surgery for stage IV colorectal cancer with synchronous peritoneal metastasis

Background: Peritoneal metastasis is well-known as a poor prognostic factor in patients with colorectal cancer. It is important to improve the prognosis of patients with colorectal cancer and synchronous peritoneal metastasis. This study aimed to clarify the factors affecting R0 resection and the prognosis of colorectal cancer patients with synchronous peritoneal metastasis. Methods: We investigated the data of patients with stage IV colorectal cancer between 1991 and 2007 in 16 hospitals that were members of the Japanese Society for Cancer of the Colon and Rectum. Results: Of the 564 colorectal cancer patients with synchronous peritoneal metastases, 341 also had hematogenous metastases. The 5-year overall survival rates in patients with and without R0 resection were 32.4 and 4.7 %, respectively. A Cox proportional hazards model showed that histologic type of poorly differentiated adenocarcinoma, regional lymph node metastasis, liver metastasis, chemotherapy after surgery, R0 resection, the Japanese classification of peritoneal metastasis, and the size of peritoneal metastases were independent prognostic factors. Of the 564 patients, 28.4 % had R0 resection. The Japanese classification of peritoneal metastasis (P1-P2, p = 0.0024) and absence of hematogenous metastases (p < 0.0001) were associated with R0 resection. Conclusions: P1-P2 peritoneal metastasis and the absence of hematogenous metastasis were the most favorable factors benefiting from synchronous resection of peritoneal metastasis. In addition, chemotherapy after surgery was essential.