Among 125 patients with peritoneal dissemination (P1-3) of colorectal cancer, including those with other synchronous metastases, the 5-year overall survival (OS) rate was 13.3% for P1 patients (n=30), 12.8% for P2 patients (n=39), and 1.8% for P3 patients (n=56) (P1 vs. P2, p=N.S.; P2 vs. P3, p=0.02; P1 vs. P3, p=0.001), while the median survival time (MST) was 12.0, 14.1, and 3.1 months, respectively. The 5-year OS rates for patients who had peritoneal dissemination without other metastases were 17.6% (n=17), 12.5% (n=19), and 3.4% (n=28) (P1 vs. P2, p=N.S.; P2 vs. P3, p=N.S.; P1 vs. P3, p=0.039), while the MST was 25.1, 15.1, and 12.5 months, respectively. In the P3 short survival group (SSG; n=13), TS expression was high in 7.7% (1/13) and low in 92.3% (12/13) of tumors, while DPD expression was high in 38.5% (5/13) and low in 61.5% (8/13) of tumors. In the P3 long survival group (LSG; n=15), the corresponding values were 80.0% (12/15), 20.0% (3/15), 33.3% (5/15), and 66.7% (10/15). High TS and low DPD expression was found in only 7.7% (1/13) of the SSG tumors vs. 46.7% (7/15) of the LSG tumors (p=0.028). These results suggest that the prognosis of stage IV colorectal cancer with P3 peritoneal dissemination is extremely poor. In addition, patients fitting the SSG criteria are unlikely to respond to treatment with 5-FU+LV, and may need combination chemotherapy using CPT-11 and/or L-OHP.

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