Long-term prognostic value of positive peritoneal washing in colon cancer

Background: We examined the potential prognostic value of free malignant cells in the peritoneal cavity of patients with colon adenocarcinoma. Methods: In 1991 and 1992, 88 patients underwent peritoneal washing with cytologic analysis immediately before elective colon resection for adenocarcinoma with no evidence of peritoneal metastases. Peritoneal washing fluid was collected before abdominal exploration, centrifuged immediately, and stained with the May-Grunwald-Giemsa and Harris Shorr methods. Malignancy was defined as recommended by Papanicolaou. Results: Free malignant cells in peritoneal fluid (positive peritoneal washing) were found in 25 of 88 (28%) patients (Dukes A, 0 of 11; Dukes B, 10 of 31; Dukes C, 11 of 37; Dukes D, 4 of 9). The positivity rate was 24 of 75 (32%) among patients with rumours involving the serous layer and 1 of 13 (8%) among the others (P = 0.0989). With a follow-up of 66.7 to 78.7 months the 5-year survival rates were 48% (95% confidence interval, 28.4-67.6) and 68% (95% CI, 56.2-79.8) among patients with positive and negative peritoneal washing, respectively (P = 0.09). Positive peritoneal washing was not significantly associated with survival in multivariate analysis. Conclusion: The presence of free malignant cells in the peritoneal cavity of patients with colon cancer provided no further prognostic information relative to the Dukes classification in this study. Nevertheless, further study is needed, particularly in a larger series of Dukes B patients, for whom a new prognostic factor would be useful for deciding adjuvant therapy.