Predominance of Peritoneal Metastasis in the Recurrence Pattern of T4 Colorectal Cancer: A Retrospective Cohort Study

Peritoneal metastasis (PM) following curative resection for colorectal cancer (CRC) remains difficult to detect and is associated with limited therapeutic options. This study aimed to assess recurrence patterns of PM after curative CRC surgery and to identify associated risk factors.

A retrospective cohort study included 4695 patients with pathologically confirmed T3 or T4 CRC who underwent curative resection at a tertiary center from January 2012 to December 2020. Recurrence site distribution, cumulative incidence of recurrence, cumulative incidence of peritoneal metastasis (CIPM), and risk factors for PM were analyzed by T stage.

Of 4,695 patients, 749 had T4 CRC, with a higher recurrence rate than T3 cases (30.6% vs. 11.9%). In T4 CRC, PM was the most common recurrence site (10.9%), surpassing lung (9.6%) and liver (7.1%) metastases. Peritoneal metastasis rates were highest in right-sided T4 colon cancers (15.7%). The 5-year CIPM was significantly higher in T4 than in T3 (11.5% vs. 1.8%, p < 0.001). Stratified analysis showed a higher cumulative incidence of PM in T4N0 disease compared with T3N+ disease (7.4% vs. 2.9%, p < 0.001). Independent risk factors for PM included T4 stage (hazard ratio 4.47; 95% confidence interval 3.15-6.35), nodal positivity (hazard ratio 2.41; 95% confidence interval 1.60-3.63), advanced age, preoperative obstruction, right-sided cancer, signet ring cell carcinoma, and perineural invasion.

Pathologic T4 CRC exhibits a distinct recurrence pattern characterized by a predominance of peritoneal metastasis. These findings may inform future surveillance protocols and treatment planning.