Peritoneal cytology does not increase the prognostic information provided by TNM in gastric cancer.

Background: This study aimed at verifying whether peritoneal cytology could improve the prognostic information provided by TNM staging in gastric cancer patients.
Method: The presence of free peritoneal tumor cells was investigated in 168 patients who underwent curative resection for gastric cancer from January 1992 to July 2002 in Verona, Italy. The influence of peritoneal cytology on survival was evaluated by a Cox regression model, controlling for potential confounders.
Results: Twenty-three patients (14%) had positive peritoneal cytology. Patients with positive lavage were more likely to present serosal infiltration (100 vs. 46%) and nodal metastases (91 vs. 67%; P < 0.001). Positive lavage was associated with a very poor prognosis: 3-year survival was only 9% (95% CI 2-27%) when peritoneal cancer cells had been detected, whereas survival reached 50% (95% CI 42-59%) in patients with a negative cytology. In multivariate survival analysis, peritoneal cytology was an independent predictor of mortality when controlling for sex, age, site, histology, and nodal metastases, but not when adjusting also for depth of tumor invasion (RR of positive versus negative = 1.2, 95% CI 0.7-2.0). Similarly, the influence of peritoneal cytology on survival was no longer significant when univariate analysis was restricted to T3/T4 patients (RR = 1.5, 0.9-2.5).
Conclusions: Positive peritoneal cytology was a marker of poor prognosis in gastric cancer patients. Nevertheless, peritoneal lavage did not increase the prognostic information already provided by the TNM staging system in this Italian series.