Abstract
BACKGROUND: The effect of claudin 18.2 (CLDN18.2) expression on the outcomes of a first-line immune checkpoint inhibitor (ICI)-containing chemotherapy (ICI-chemo) in patients with human epidermal growth factor receptor 2 (HER2)-negative, proficient mismatch repair (pMMR), and programmed death-ligand 1 (PD-L1)-expressing metastatic or recurrent gastric or gastroesophageal junction cancers (mGC/GEJC) remains unclear. OBJECTIVES: We assessed the effects of CLDN18.2 expression on the outcomes of first-line ICI-containing chemotherapy in patients with HER2-negative, pMMR, and PD-L1-expressing mGC/GEJC. PATIENTS AND METHODS: Medical records of patients with HER2-negative, pMMR, and PD-L1 combined positive score (CPS) ⩾1 unresectable/metastatic or recurrent GC/GEJC who received first-line ICI-chemo or chemotherapy alone (chemo-alone) between January 2016 and August 2024 were retrospectively analyzed. The impact of CLDN18.2 status on the clinical outcomes was evaluated in patients receiving ICI-chemo and chemo-alone to assess the prognostic significance of CLDN18.2 in the absence of ICI. RESULTS: A total of 150 patients were treated with ICI-chemo, whereas 313 patients received chemo-alone. CLDN18.2 positivity (⩾2+ in ⩾75% tumor cells) was identified in 42 patients (28.0%) in the ICI-chemo group and 94 patients (30.0%) in the chemo-alone group. There were no significant differences in the objective response rate (ORR; 68.3% vs 70.3%, p = 0.842), disease control rate (DCR; 92.7% vs 94.1%, p = 0.718), progression-free survival (PFS; hazard ratio (HR) 1.01, p = 0.955), or overall survival (OS; HR 1.12, p = 0.615) between CLDN18.2-positive and CLDN18.2-negative patients in the ICI-chemo group. Similarly, the DCR, ORR, PFS, and OS outcomes were comparable between the CLDN18.2-positive and -negative patients in the chemo-alone group. CONCLUSION: CLDN18.2 expression exerted no impact on outcomes of first-line ICI-chemo and chemo-alone in patients with HER2-negative, pMMR, and PD-L1 CPS ⩾1 mGC/GEJC.