Factors Affecting the Prognosis after Primary Tumor Resection for Patients with Metastatic Colorectal Cancer with Synchronous Peritoneal Metastasis: A Multi-center, Prospective, Observational Study.

OBJECTIVES

To clarify the risk factors affecting prognosis after primary tumor resection (PTR) in patients with metastatic colorectal cancer with synchronous peritoneal metastasis (mCRC-SPM).

METHODS

Patients were enrolled prospectively in the JSCCR project "Grading of Peritoneal Seeding in Colorectal Cancer." Factors that may influence overall survival-age, sex, location of the primary tumor, lymph node metastasis, presence of liver metastasis, degree of peritoneal metastasis, peritoneal cancer index (PCI), cancer cure, and postoperative chemotherapy-in the PTR group were examined using multivariate analysis.

RESULTS

Of the 133 enrolled patients with mCRC-SPM, 112 patients underwent PTR. Among them, 26 (23.2%) had mCRC-SPM of grade P1, 47 (42.0%) of P2, and 39 (34.8%) of P3. The median PCI was 4 (range, 1-28); no surgery-related deaths occurred. Postoperative complications of Clavien-Dindo classification ≥grade 2 were observed in 20 (17.9%) patients. R0 surgery became more difficult as the degree of dissemination increased, and the PTR group had a significantly better prognosis than the non-PTR group. In the multivariate analysis, age ≥75 years, rectal cancer, presence of liver metastasis, higher PCI, non-curative resection, and non-treatment with systemic chemotherapy were associated with poor prognosis in patients after PTR.

CONCLUSIONS

In patients with mCRC-SPM, postoperative complications are infrequent for P1 with localized peritoneal dissemination, and PTR may be considered as aggressive treatment. Factors including age ≥75 years, rectal cancer, presence of liver metastasis, increased PCI, non-curative resection, and non-treatment with systemic chemotherapy are associated with a reduced survival benefit from PTR.