A Sequential Trial of Low-Dose Radiotherapy Followed by Concurrent Immunotherapy, Systemic Chemotherapy, and Intraperitoneal Perfusion in Gastric Cancer With Peritoneal Carcinomatosis

Overview

This study is a prospective, single-center, open-label, exploratory phase II clinical trial aimed at evaluating the safety, tolerability, and preliminary efficacy of low-dose radiotherapy (LDR) sequentially combined with serplulimab, bevacizumab analog, and irinotecan or albumin-bound paclitaxel in patients with gastric cancer and peritoneal metastases. A total of 40 patients with gastric adenocarcinoma who have previously undergone first-line therapy are planned for enrollment. Patients will be grouped based on prior exposure to paclitaxel-based chemotherapy to determine whether they will receive systemic treatment with irinotecan combined with serplulimab or albumin-bound paclitaxel combined with serplulimab, along with local intraperitoneal infusion of bevacizumab analog. The study adopts a Simon two-stage design, with 20 patients enrolled in the first stage. If ≥3 patients achieve objective remission, the study will proceed to the second stage, enrolling an additional 20 patients.

In China, most gastric cancer patients are diagnosed at an advanced stage. The peritoneum is the most common site of metastasis for gastric cancer, representing a specific mode of metastasis. Based on cytology of abdominal cavity dropout cells and peritoneal implantation formation, it can be classified into CY1P0, CY1P1, and CY0P1 types. Approximately 20% of patients are diagnosed with peritoneal metastasis preoperatively or intraoperatively, and more than 50% of T3 and T4 stage patients develop peritoneal metastasis after radical surgery. Peritoneal metastasis often leads to malignant ascites, intestinal obstruction, cancer pain, and other complications, severely affecting the quality of life of patients. According to epidemiological data, in 2020, the number of gastric cancer patients with peritoneal metastasis in China reached 523,937 cases 3-6 months, and a 5-year survival rate of less than 2% . Effective control of ascites in gastric cancer patients can not only improve their quality of life but also effectively extend their survival time. The survival period for first-line gastric cancer patients with peritoneal metastasis has increased from 3-6 months with traditional chemotherapy to 12-22 months with comprehensive treatment , but the efficacy for second-line gastric cancer patients with peritoneal metastasis remains limited, and more effective treatment regimens are still needed. Vascular endothelial growth factor (VEGF) plays a central role in angiogenesis and ascites formation in peritoneal metastases. Research evidence shows that intraperitoneal infusion of anti-VEGF drugs, such as bevacizumab, can effectively control ascites and prolong the time to ascites recurrence. When combined with the immune checkpoint inhibitor sintilimab, the ascites control rate can reach 91%, with partial reduction of peritoneal metastases by more than 30% in some patients. Analysis of immune cells in ascites showed that the CD8+/Treg ratio increased threefold after treatment (P\<0.01), and immunohistochemistry results from peritoneal biopsy indicated upregulation of PD-L1 expression in the combination therapy group (combination group vs baseline: +45% vs +10%), suggesting that blocking VEGF can normalize tumor vasculature, reverse the immunosuppressive microenvironment, enhance T-cell infiltration, and exert synergistic effects study, are actively exploring whether combining immunotherapy with VEGFR inhibitors and chemotherapy can improve survival, but further investigation is still needed. Recent research findings indicate that low-dose radiation therapy (Low-Dose Radiation, LDR, single dose ≤1 Gy) exhibits distinct biological effects compared to conventional radiation therapy (fractionated dose1.8-3 Gy)20.LDR not only does not cause significantDNA double-strand breaks and apoptosis but also remodels the tumor microenvironment by activating various immune-related pathways. Based on the aforementioned background, this study proposes an innovative combination therapy strategy: low-dose radiotherapy (LDR) followed by immunochemotherapy. The core mechanisms are as follows: (1) Immune initiation effect: LDR acts as an "immune initiator," inducing immunogenic cell death and activating antigen-presenting cells. The peak of immune activation occurs 24-72 hours after LDR, during which administration of the PD-1 inhibitor (serplulimab) can maximize synergistic effects. (2) Vascular normalization window: A peak in vascular normalization is observed 7-14 days after LDR treatment. Combining anti-VEGF drugs (bevacizumab analog) can maintain the vascular normalization state and improve the distribution of chemotherapeutic drugs in metastases to the peritoneum. (3) Overcoming chemotherapy resistance: LDR downregulates the expression of DNA repair genes in tumor cells, enhancing the cytotoxic action of irinotecan and albumin-bound paclitaxel. Preclinical studies show that 0.5 Gy radiotherapy can increase the concentration of paclitaxel in metastases to the peritoneum by 2.8 times. This study selected low-dose radiotherapy combined with intraperitoneal infusion of bevacizumab. Based on whether first-line chemotherapy regimens included intravenous chemotherapy with albumin-bound paclitaxel, patients were chosen to receive second-line systemic treatment with irinotecan/albumin-bound paclitaxel combined with serplulimab. The study explores the approach of immune rechallenge and low-dose radiotherapy sequential systemic treatment combined with intraperitoneal infusion therapy, aiming to provide new therapeutic strategies and methods for second-line patients with gastric cancer accompanied by peritoneal metastasis.