Quantitative molecular diagnosis of peritoneal lavage fluid for prediction of peritoneal recurrence in gastric cancer

We developed a quantitative multiple-marker RT-PCR assay for sensitive detection of free cancer cells in the peritoneal cavity and examined the significance of this molecular diagnostic technique for detection and prediction of peritoneal dissemination in patients with gastric cancer. Preoperative peritoneal lavage fluid samples obtained from 129 patients with gastric cancer were subjected to RT-PCR assay with primers specific for carcinoembryonic antigen (CEA) and cytokeratin-20 (CK-20), and conventional cytological examination with Papanicolaou staining. The multi-marker RT-PCR assay was positive in 59 of 129 (46%) gastric cancer patients, whereas conventional cytology was positive in only 9 of 129 (7%) patients. Thirty-two of 129 (22%) patients suffered disease recurrence after surgery. Twenty-one of these patients were confirmed to have had peritoneal recurrence. Although conventional cytology was positive on peritoneal washes in only 9 patients, the RT-PCR assay was positive in 20 of these 21 patients. Furthermore, in cases with negative cytology, patients with PCR-positive findings in peritoneal lavage fluid had a significantly poorer prognosis than those with negative PCR, mainly because of peritoneal recurrence. Our results suggest that the multiplex RT-PCR assay for CEA and CK-20 was highly sensitive for detection and might be useful for prediction of peritoneal dissemination in gastric cancer.