Introduction: Detection of malignant cells in the peritoneal cavity indicates the extension of cancer cells. The aim of this study is to evaluate the incidence rate of positive cytology in colorectal cancer and its relationship with the local progress of the tumor. 

Methods: In a 2-year prospective study in Mashhad and Iran Universities of Medical Sciences, peritoneal lavage was performed on 40 patients with colorectal cancer from May 2012 to May 2013. Before any manipulation of the abdominal cavity, about 100 cc of normal saline was entered into the peritoneal cavity. Then, the samples were submitted for cytology. A sample was considered as positive if at least one cancer cell was detected.  

Results: From among 40 patients, 19 were male and 21 were female. The mean age of the patients was 51 years. They consisted of 17 cases of colon cancer and 23 cases of rectal cancer. Totally, positive cytology was identified in three patients. Among them, one case had abdominal carcinomatosis and the other two cases were involved at the levels of T3 and/or T4.

conclusions: It appears that peritoneal cytology is an appropriate method to evaluate tumor staging. Results of this method can be correlated between positive cytology and peritoneal seeding and survival, although the result of negative cytology cannot exclude advanced colorectal cancer and patients with carcinomatosis may have a negative peritoneal lavage.