An exploratory phase II trial of low-dose decitabine and sintilimab combined with chemotherapy in HER2-negative gastric or gastroesophageal junction adenocarcinoma.

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390 Background: Combining epigenetic modulator with PD-1 inhibitor may enhance treatment outcomes in cancer patients. This study aimed to evaluate the efficacy and safety of epigenetic drug decitabine, sintilimab (a PD-1 inhibitor), and chemotherapy in gastric cancer. Methods: In this single-arm, exploratory phase II trial, patients with HER2-negative, locally advanced or metastatic gastric or gastroesophageal junction (G/GEJ) adenocarcinoma were enrolled between August 12, 2021, and October 22, 2022. Treatment included low-dose decitabine (10 mg/m² for 5 days), sintilimab (a PD1 inhibitor, 200 mg every 21 days), and XELOX. The primary endpoint was objective response rate (ORR) and second endpoints included disease control rate (DCR), progression-free survival (PFS), overall survival (OS), and safety. The protocol was approved by the ethics committee of the Changzhi Medical College Affiliated Changzhi People's Hospital (No. 2021K002). All patients provided written informed consent form before study participation. The trial is registered with Chinese Clinical Trial, number ChiCTR2100043312. Results: Sixteen patients were initially enrolled, with a median follow-up of 14.8 months. Eleven patients exhibited a PD-L1 combined positive score (CPS) < 5. In the per-protocol sets, 11 patients remained eligible for efficacy analysis. In the intention-to-treat analysis of all 16 patients, 9 achieved partial response and 2 had stable disease, resulting in an ORR of 69% and a DCR of 56%. As of the data cutoff on November 4, 2023, the median PFS was 11.1 months (95% CI, 5.1-not reached) and the median OS was 13.2 months (95% CI, 5.1-not reached). Treatment-related adverse events were generally well-tolerated, with most being grade 1-2. Three patients experienced severe AEs, including one fatal case of grade 4 immune-related pneumonia. Conclusions: The combination of low-dose decitabine, sintilimab, and chemotherapy appears promising strategy for locally advanced or metastatic G/GEJ adenocarcinoma, especially in patients with negative HER2 and low PD-L1 expression. These preliminary findings support further investigations to confirm the benefits and explore the underlying mechanisms. Clinical trial information: ChiCTR2100043312. Objective response and disease response. Full analysis set (n=16) Efficacy analysis set (n=11) Complete response 0 0 Partial response 9 9 Stable disease 2 2 Progressive disease 0 0 Non-evaluable* 5 NA Objective response 9 (56%) 9 (81.8%) Disease control 11 (69%) 11 (100%) NA=not applicable. *Included patients without any post-baseline response assessment.