In colorectal cancer, the role of detecting free malignant cells from peritoneal lavage is currently unclear. In this study, we investigated the positive rate of free malignant cells in peritoneal lavage fluid and their predictive value for prognosis and peritoneal recurrence after a curative resection.

From October 2009 to December 2011, in a prospective manner, we performed cytologic examinations of peritoneal lavage fluid obtained just after the abdominal incision from 145 patients who underwent curative surgery for colorectal cancer. We used proportional hazard regression models to analyze the predictive role of positive cytology for peritoneal recurrence and survival.

Among total 145 patients, six patients (4.1%) showed positive cytology. During the median follow-up of 32 months (range, 8-49 months), 27 patients (18.6%) developed recurrence. Among them, 5 patients (3.4%) showed peritoneal carcinomatosis. In the multivariate analysis, positive cytology was an independent predictive factor for peritoneal recurrence (hazard ratio [HR], 136.5; 95% confidence interval [CI], 12.2-1,531.9; P < 0.0001) and an independent poor prognostic factor for overall survival (HR, 11.4; 95% CI, 1.8-72.0; P = 0.009) and for disease-free survival (HR, 11.1; 95% CI, 3.4-35.8; P < 0.0001).

Positive cytology of peritoneal fluid was significantly associated with peritoneal recurrence and worse survival in patients undergoing curative surgery for colorectal cancer. Peritoneal cytology might be a useful tool for selecting patients who need intraperitoneal or systemic chemotherapy.

The aim of this study was to investigate the clinicopathologic features of and the prognosis for colorectal cancers (CRCs) with microsatellite instabilities (MSIs).

Between 2006 and 2009, genotyping was performed on 245 patients with stage II/III CRCs to establish the MSI status. The clinicopathologic differences and the prognostic value of MSI were analyzed. The median follow-up period was 38 months (range, 7-68 months).

Of the total 245 patients, 20 (8.2%) had MSI-high (H) and 225 (91.8%) had MSI-low (L) or stable (S) CRCs. Adjuvant chemotherapies were performed on 101 stage II (87.8%) and 107 stage III patients (82.3%). Patients with MSI-H CRCs more frequently had a family history of colon cancer (10% vs. 2.7%, P = 0.003), more frequently had a cancer located at the proximal colon (90.0% vs. 19.1%, P < 0.0001), and more often showed a mucinous phenotype or poor differentiation (35.0% vs. 7.1%, P = 0.001). Despite less frequent lymph node metastasis (25% vs. 55.6%, P = 0.01), the number of retrieved lymph nodes was higher (26.3 ± 13.1 vs. 20.7 ± 1.2, P = 0.04) in the MSI-H group. The overall survival and the disease-free survival (DFS) did not differ with respect to MSI status. However, in the stage II subgroup, the DFS for patients with MSI-H CRCs was significantly worse (72.2% vs. 90.7%, P = 0.03). The multivariate analysis performed on this subgroup revealed that MSI-H was an independent poor prognostic factor (adjusted hazard ratio, 4.0; 95% confidence interval, 1.0-15.6, P = 0.046).

MSI-H CRCs had distinct clinicopathologic features, and MSI-H was an independent poor prognostic factor in stage II CRCs. Considering the majority of stage II patients were administrated adjuvant chemotherapy, the efficacy of adjuvant chemotherapy for treating MSI CRCs might be different from that for treating MSI-L/S tumors.