TPS160 Background: Up to 50% of patients with gastric cancer (GC) may develop peritoneal metastasis (PM) that is associated with resistance to systemic therapy and poor prognosis. Although cytoreductive surgery and intraperitoneal (IP) chemotherapy were shown to modestly improve the survival of patients with PM from gastric GC (PM-G), these clinical trials were performed in the pre-immunotherapy era. The significant heterogeneity in trial design and patient selection criteria further limit the applicability of these trial results to current clinical practice where anti-PD-1/L1 immunotherapy and/or targeted therapy in combination with chemotherapy have become a common, standard first-line therapy for the majority of patients with metastatic GC, raising the question of whether chemotherapy such as paclitaxel remains the most effective IP therapy. IP therapy using novel immunotherapy such as bispecific antibodies and chimeric antigen receptor T-cell therapy have demonstrated safety and promising antitumor activities in PM-G. We are conducting a phase 1b clinical trial that evaluates the efficacy of IP interleukin-2 (IL-2) in patients with PM-G with stable disease on first-line chemo-immunotherapy based on the hypothesis that IP IL-2 may synergize with intravenous (IV) chemo-immunotherapy to improve the treatment of PM-G. Multi-omics studies using patient blood, peritoneal fluid, and tissue specimens serially collected from this trial will be performed to characterize the changes in the tumor immune microenvironment of PM-G and identify new therapeutic targets. Methods: Patients with PM only from gastric adenocarcinoma are eligible for this phase 1b trial. All participants will continue IV fluorouracil-containing chemotherapy with nivolumab every 2 weeks and concurrently receive up to 16 doses of IP IL-2 (aldesleukin 6 × 10 5 IU/m2) weekly through an indwelling peritoneal catheter (Bard). Diagnostic laparoscopy (DL) will be performed before initiation of IP IL-2 and after 8 doses of IP therapy to assess treatment response based on the peritoneal cancer index (PCI), which is the primary endpoint of the trial. Patients with at least stable radiographic disease will continue to receive another 8 doses of IP IL-2 and undergo a third DL. Secondary endpoints include safety, peritoneal regression grading score, overall survival, and progression-free survival. Major inclusion criteria include mismatch repair-proficient or microsatellite-stable GC, PCI of 3-24, absence of distant metastasis other than PM, stable disease on first-line IV chemo-immunotherapy, tolerability of anti-PD-1 therapy, and adequate organ function. Enrollment began in 2024 and remains active. To date, seven of planned 15 patients have received study treatment without significant treatment-related adverse events and three of these patients underwent curative-intent cytoreductive surgery. Clinical trial information: NCT05802056 .
Zhu et al. (Tue,) studied this question.