Outcomes of patients with peritoneal-limited metastatic gastric cancer (PLGC) undergoing bidirectional (BD) chemotherapy cytoreductive surgery (CRS) with heated intraperitoneal chemotherapy (HIPEC).

328 Background: The prognosis of PLGC patients (pts) is poor with standard systemic therapy. PLGC pts who undergo CRS after BD chemotherapy (chemo) demonstrate prolonged survival. We retrospectively analysed the outcomes of pts who underwent BD chemo followed by CRS and HIPEC in a single institution, stratifying by peritoneal carcinomatosis index (PCI) and chemo regimen. Methods: PLGC pts who received BD chemo between January 2016 to September 2023 were enrolled and consented for data collection. BD chemo was either 3 weekly paclitaxel (PTX) (50mg/m2), S-1 (80mg/m2) and IP PTX (20mg/m2) or capecitabine (2g/m2), oxaliplatin (100mg/m2) (CAPOX) and IP PTX (40mg/m2). HIPEC utilised cisplatin 50mg/m2 at 40 for 60 minutes. Trastuzumab and nivolumab were given selectively. Pts without radiological progression after 24 weeks of BD chemo, with PCI7 and potential for complete resection underwent CRS including D2 gastrectomy and HIPEC. Post-resection, BD chemo was stopped. Survival was analysed by Kaplan Meier curves, adverse events (AEs) by CTCAE v5.0 and response by independent radiological review. Results: 34 pts were enrolled with median follow-up of 26.9 months (m). Median (range) age was 51 (17 – 79) and median PCI 12 (0-29). 52.9% were female, 8.8% had Cy1 only disease and 38% had prior gastrectomy. 3 out of 6 pts with evaluable disease had partial response. Median progression-free survival and overall survival (mOS) was 9.1m and 16.5m respectively. 7 pts (20.6%) underwent CRS with median (range) PCI of 1 (0-15.0). mOS in CRS vs non-CRS pts was 23.8m vs 14.6m (p=0.4); PCI <7 vs PCI ≥7 was 23.8m vs 14.6m (p=0.63); and CAPOX vs S1/PTX systemic chemotherapy was 23.9m vs 14.6m (p=0.29) respectively. Peritoneal cytology negativity increased from 25.8% to 86.4% after BD chemo. Peritoneal lesions biopsied post-BD chemo showed no tumour cells in 64% of cases. There was no treatment-related mortality. 1 pt had IP port removal due to complications. The commonest grade 3 AE was neutropenia (14.7%). Biomarker analysis is currently being performed. Conclusions: BD chemo CRS HIPEC was well tolerated with longer survival in patients undergoing CRS. Evaluation of tumour using PCI post-BD chemo may be sub-optimal.