Investigation of the Japanese Classification of Peritoneal Metastasis from Colorectal Cancer Referring to the Correlation with PCI

Cytoreductive surgery for synchronous and metachronous colorectal peritoneal dissemination: Japanese P classification and peritoneal cancer index

Aim

The outcomes of cytoreductive surgery (CRS) for synchronous and metachronous colorectal peritoneal dissemination were investigated using the Japanese P classification and peritoneal cancer index (PCI).

Methods

CRS was performed in 111 cases of synchronous peritoneal dissemination and 115 cases of metachronous peritoneal dissemination. The P classification and PCI were determined at the time of laparotomy.

Results

In the synchronous dissemination group, the 5-year overall survival rates after CRS in P1/P2 and P3 cases were 51% and 13%, respectively. Even for P3, 51% of the patients achieved macroscopic cytoreductive complete resection (CC-0), with a 5-year survival rate of 40%. When P3 cases were classified into PCI 0-9, 10-19, 20-29, and 30-39, CC-0 was achieved in 93%, 70%, 6%, and 0% of the cases, respectively, and the 5-year survival rate of PCI 0-9 was 41%. In the metachronous dissemination group, the 5-year survival rates were 62% for PCI 0-9 and 22% for PCI 10-19; 5-year survival was not observed in patients with a PCI ≥ 20. CC-0 was significantly associated with the postoperative prognosis in both synchronous and metachronous peritoneal dissemination.

Conclusion

In cases of synchronous dissemination, CRS must be performed for P1 and P2 cases or those with a PCI < 10, while detailed examination using PCI is required for P3 cases. In cases of metachronous dissemination, CRS should be considered when the PCI score is <20.

A proposed new Japanese classification of synchronous peritoneal metastases from colorectal cancer: A multi-institutional, prospective, observational study conducted by the Japanese Society for Cancer of the Colon and Rectum

Aim

To establish a new Japanese classification of synchronous peritoneal metastases from colorectal cancer.

Methods

This multi-institutional, prospective, observational study enrolled patients who underwent surgery for colorectal cancer with synchronous peritoneal metastases. Overall survival rates were compared according to the various models using objective indicators. Each model was evaluated by Akaike's information criterion (AIC). The region of peritoneal metastases was evaluated by the peritoneal cancer index (PCI).

Results

Between October 2012 and December 2016, 150 patients were enrolled. The AIC of the present Japanese classification was 1020.7. P1 metastasis was defined as confined to two regions. The minimum AIC was obtained with the cutoff number of 10 or less for P2 metastasis and 11 or more for P3 metastasis. As for size, the best discrimination ability between P2 and P3 metastasis was obtained with a cutoff value of 3 cm. The AIC of the proposed classification was 1014.7. The classification was as follows: P0, no peritoneal metastases; P1, metastases localized to adjacent peritoneum (within two regions of PCI); P2, metastases to distant peritoneum, number ≤10 and size ≤3 cm; P3, metastases to distant peritoneum, number ≥11 or size >3 cm; P3a, metastases to distant peritoneum, number ≥11 and size ≤3 cm, or number ≤10 and size >3 cm; P3b, metastases to distant peritoneum, number ≥11 and size >3 cm.

Conclusion

This objective classification could improve the ability to discriminate prognosis in patients with synchronous peritoneal metastases from colorectal cancer.