Long-Term Prognostic Value of Conventional Peritoneal Lavage Cytology in Patients Undergoing Curative Colorectal Cancer Resection

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Free malignant cells in the peritoneal cavity might play a role in the metastasis process. However, this phenomenon needs further elucidation. The aims of this study were to investigate the frequency of free cancer cells detected on cytologic examination of lavage fluid after peritoneal washing in patients undergoing curative surgery for colorectal cancer, to explore risk factors for exfoliation of cancer cells into the peritoneal cavity, and to evaluate the influence peritoneal lavage cytology as a prognostic tool. Peritoneal lavage was performed in 697 patients undergoing curative resection of colorectal cancer. Before the manipulation of the tumor, 100 mL of physiologic saline solution was administered into the abdominal cavity and the fluid was collected for cytologic examination. Specimens were classified as positive if at least one cancer cell was detected. The mean follow-up period was 90.5 months. Overall, 15 (2.2%) of the 697 patients had positive results. Four characteristics were identified as risk factors for exfoliation of cancer cells into the peritoneal cavity: 1) depth of invasion, 2) regional lymph nodes, 3) lymphatic invasion, and 4) venous invasion. In univariate analyses of all 697 patients and the subgroup of 374 patients with pT3 or T4 tumors, patients with positive cytology findings had significantly worse disease-free and cancer-specific survival than patients with negative cytology findings (P < 0.001). On multivariate analysis, peritoneal cytology remained an independent predictor of cancer-specific survival in all patients and in patients with pT3 or pT4 tumors. Only peritoneal cytology was a significant prognostic factor for peritoneal recurrence (P < 0.0001). Conventional peritoneal cytology is a useful prognostic tool in patients undergoing curative surgery for colorectal cancer and may be helpful in making decisions whether to select intraperitoneal or systemic chemotherapy.