Clinical Significance of Cytological Status of Peritoneal Lavage Fluid During Intraperitoneal Chemotherapy for Gastric Cancer with Overt Peritoneal Dissemination

Background. A positive cytology of peritoneal lavage fluid (CY1) is a poor prognostic factor in patients with gastric cancer (GC). We have recently reported that CY1 often changes to negative (CY0) following combination chemotherapy including intraperitoneal (IP) paclitaxel (PTX), which results in marked prolongation of survival in GC patients with peritoneal dissemination (P1). Methods. A total of 95 P1 GC patients who received combination chemotherapy with S-1 and intravenous and IP PTX were enrolled. Peritoneal lavage fluid was periodically examined cytologically at the start of every cycle of chemotherapy, and the impact of CY status on patient outcome was retrospectively evaluated. Results. Seventy-three (76.8 %) of 95 patients were diagnosed as CY1 before initial treatment. Median survival time (MST) of the CY1 group was significantly shorter than that of the CY0 group (19.1 vs. 32.5 months, P = 0.033). Cytological status changed from CY1 to CY0 in 68 (93.2 %) of 73 CY1 patients during the whole treatment period and MST of patients who showed a negative change was significantly longer than that of the unchanged group (20.0 vs. 13.0 months, P = 0.0017). In 64 patients who achieved CY0 by IP PTX regimen, the median time to achieve CY0 was 1.4 months, and patients who achieved a negative change within 1 month showed a particularly good outcome (MST = 26.1 months). Conclusions. Periodic cytological examination of peritoneal lavage fluid is clinically useful to evaluate the efficacy of treatment as well as to predict the outcome of patients with P1 GC.