Mechanisms of peritoneal metastasis after operation for non-serosa-invasive gastric carcinoma: an ultrarapid detection system for intraperitoneal free cancer cells and a prophylactic strategy for peritoneal metastasis.

PURPOSE This aims of this study are to establish an ultra-rapid quantitative reverse transcription-PCR (RT-PCR) protocol that enables the diagnosis of i.p. cancer spread during operation, to reveal the mechanisms of peritoneal metastasis from non-serosa-invasive gastric carcinoma, and to evaluate the effect of the extensive intraoperative peritoneal lavage (EIPL) using the ultra-rapid quantitative RT-PCR as a prophylactic strategy for peritoneal metastasis. EXPERIMENTAL DESIGN Peritoneal lavage samples from 63 patients with non-serosa-invasive gastric carcinoma were obtained at laparotomy and immediately after lymph node dissection. To identify the free cancer cells in the samples, carcinoembryonic antigen- and cytokeratin 20-specific RT-PCRs were performed using the LightCycler method in combination with an automated mRNA extractor. In addition, EIPL was performed in five cases with serosa-invasive gastric carcinoma, and its efficacy was evaluated by the ultra-rapid quantitative RT-PCR protocol. RESULTS The method enabled us to complete the detection of cancer cells within approximately 70 min. Both the carcinoembryonic antigen and cytokeratin 20 mRNA in i.p. lavages after lymph node dissection were identified in three (14.3%), four (26.7%), and six (46.2%) patients with submucosal, muscularis propria, and subserosal tumors, respectively. Lymph node metastasis was the independent predictor of the existence of i.p. free cancer cells. The ultra-rapid quantitative RT-PCR demonstrated that EIPL reduced free cancer cells from 3.8 x 10(5) +/- 1.4 x 10(5) cells to 2.8 +/- 1.5 cells/100 ml lavage after six to eight washes, and they disappeared after seventh to ninth wash. CONCLUSIONS The present study proved that lymph node dissection opened lymphatic channels and spread viable cancer cells into the peritoneal cavity. It is suggested that the combination of the novel detection system with the intraoperative therapy of EIPL can be a useful prophylactic strategy for peritoneal metastasis from gastric carcinoma.