e16077 Background: Patients with advanced gastric or gastroesophageal junction cancer (GC/GEJC) accompanied by peritoneal metastasis have an extremely poor prognosis, with limited treatment options and suboptimal outcomes from conventional systemic chemotherapy. Local therapy centered on hyperthermic intraperitoneal chemotherapy (HIPEC), combined with systemic treatment , has emerged as a promising approach for conversion therapy. This study aimed to evaluate the efficacy and safety of HIPEC combined with camrelizumab (a PD-1 inhibitor), paclitaxel, and S-1 in conversion therapy for patients with HER2-negative advanced GC/GEJC and peritoneal metastasis. Methods: This was a prospective, multicenter, single-arm phase II clinical study. Eligible patients had histologically confirmed advanced GC/GEJC with peritoneal metastasis (Peritoneal Carcinomatosis Index PCI score ≤20) as verified by laparoscopic exploration and no evidence of other distant metastases. All participants received conversion therapy: first, diagnostic laparoscopy followed by one cycle of HIPEC (paclitaxel 75 mg/m², days 1 and 3) within 72 hours post-surgery, along with concurrent oral S-1; subsequently, they received four cycles of systemic therapy (camrelizumab 200 mg IV on day 1 every 3 weeks + paclitaxel 150 mg/m² IV on day 1 every 3 weeks + oral tegafur on days 1–14 every 3 weeks). Radiological assessments were performed every 6 weeks. After completing five cycles of treatment, surgical feasibility was evaluated by a multidisciplinary team. Patients achieving R0 resection proceeded to receive four additional cycles of adjuvant therapy (following the same systemic regimen). The primary endpoint was the R0 resection rate; secondary endpoints included OS, PCI response rate, and safety. Results: A total of 46 patients were enrolled . Efficacy results demonstrated a conversion surgery rate of 67.4% (31/46), among whom 90.3% (28/31) achieved R0 resection, yielding an overall R0 resection rate of 60.9% (28/46). Additionally, the peritoneal carcinomatosis index (PCI) response rate (reduction in PCI score) was 69.6% (32/46). For survival outcomes, the median OS was 30 months in the surgery group versus 9.5 months in the non-surgery group (HR 0.09387; 95% CI: 0.03431 to 0.2568; p < 0.0001).Safety analysis indicated that the overall treatment regimen was tolerable: grade ≥3 TRAEs occurred in 19.6% (9/46) of patients, while the total incidence of grade 1–2 TRAEs was 73.9% (34/46). Common adverse events included hematological toxicities, gastrointestinal reactions, and irAEs such as reactive cutaneous capillary endothelial proliferation. Conclusion: HIPEC combined with camrelizumab, paclitaxel, and S-1 demonstrated promising conversion surgery and R0 resection rates, significantly improved survival outcomes in surgical patients, Clinical trial information: NCT04889768 .
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