Free peritoneal tumour cell identification in patients with gastric and colorectal cancer.

The finding of free tumour cells within the peritoneum at the time of laparotomy for gastrointestinal cancer is an important indicator of prognosis and may help select treatment. The aim of this study was to improve the methods whereby these cells could be retrieved and identified. Free peritoneal cancer cells were found in 6 out of 18 gastric cancer patients. All 6 patients had tumour invasion through to the serosa and subsequently died of tumour recurrence. None of the 18 Dukes' B and C colorectal cancer patients had free peritoneal cancer cells. Only 2 of a further 5 patients with extensive colorectal tumour spread had positive cytologies. The conventional mucin stain Periodic Acid Schiff (after diastase digestion) and the monoclonal antibody stain B72.3 were the most useful in identifying free peritoneal cancer cells. Peritoneal brushings did not offer any advantages over conventional peritoneal washings in the retrieval of free tumour cells.