The impact of pre-operative chemotherapy in patients with peritoneal lavage cytology positive or localized peritoneum metastasis for gastric cancer: A multicenter retrospective study.

95 Background: Peritoneal lavage cytology of positive and localized peritoneum metastasis of gastric cancer (GC) are defined as CY1 and P1 in the 14th edition of the Japanese Classification of GC. Patients (pts) with CY1 and/or P1 have poor prognosis after removing all macroscopically visible disease by standard gastrectomy followed by S1. The aim of this study was to investigate the efficacy of pre-operative chemotherapy (Pre-Cx) in patients with CY1 and/or P1. Methods: We retrospectively reviewed the GC pts who were diagnosed to have CY1 and/or P1 at 34 institutions participating in the Stomach Cancer Group of Japan Clinical Oncology Group between 2007 and 2012. Inclusion criteria were: no distant metastasis other than CY1 or P1, no prior treatment for GC. The subjects were divided to two groups according to treatment strategy with/without Pre-Cx before surgery. In the Pre-Cx group, status of CY and P was diagnosed by laparoscopy before and after Pre-Cx, and indication of surgical resection was decided by each physician. Results: A total of 824 pts were collected from 34 institutions. Of the 713 eligible pts, 150 pts received Pre-Cx (Pre-Cx group) and 563 pts underwent surgery followed by Cx (Post-Cx group). Proportions of P0CY1/P1CY0/P1CY1 were 69/12/19% and 69/17/14% in the Pre- and Post-Cx. Cx regimen for Pre-Cx were S1 plus cisplatin/ docetaxel and cisplatin plus S1/others (n=90/37/23). In the Pre-Cx, 57 (38%) pts who achieved P0CY0 after Pre-Cx showed better survival than the remaining 92 pts (overall survival (OS), 31.0 vs. 19.9 months (M), HR=1.99, 95% CI 1.32-2.93, p=0.001). OS was 24.8 and 24.0 M in the Pre- and Post-Cx (HR 1.07; 95% CI 0.87-1.32, p=0.502). In multivariate analysis, P1CY1, over 65 years old and clinical N3 lymph node metastasis were identified as the independent prognostic factor for OS (p<0.05). Conclusions: Although Pre-Cx showed favorable survival in case of achieving P0 and CY0, Pre-Cx did not show a survival benefit for GC pts with CY1 and /or P1.