Claudin 18.2-targeting antibody-drug conjugate CMG901 in patients with advanced gastric or gastro-oesophageal junction cancer (KYM901): a multicentre, open-label single-arm, phase 1 trial

Background CMG901 is a novel first-in-class antibody-drug conjugate with a humanised anticlaudin 18.2 antibody linked to microtubule-disrupting agent monomethyl auristatin E. We aimed to assess the antitumour activity and safety of CMG901 in patients with advanced gastric or gastro-oesophageal junction cancer and other solid tumours. Methods KYM901 is a multicentre, open-label, single-arm, phase 1 trial consisting of dose-escalation and dose- expansion stages. Patients with advanced solid tumours, including gastric or gastro-oesophageal junction and pancreatic cancers, were recruited from 31 hospital sites in China. Eligible patients were aged 18 years or older, were refractory to standard therapy or had no available standard-of-care regimen, and had an Eastern Cooperative Oncology Group performance status score of 0-1, a life expectancy of at least 3 months, and at least one measurable lesion. Patients received intravenous CMG901 every 3 weeks (0<middle dot>3-3<middle dot>4 mg/kg in dose escalation and 2<middle dot>2-3<middle dot>0 mg/kg in dose expansion) until disease progression, unacceptable toxic effects, initiation of new antitumour therapy, study withdrawal, or death. Primary endpoints were adverse events and dose-limiting toxic effects in the dose-escalation phase, and objective response rate and recommended phase 2 dose in the dose-expansion phase. Confirmed objective response was defined as a partial or complete response that was verified by follow-up imaging at least 4 weeks after the initial assessment. Safety was assessed in all patients who received at least one dose of CMG901 with at least one post-dose safety evaluation. Antitumour activity was assessed in all patients who received at least one dose of CMG901 (full analysis set) and in all CMG901-treated patients with at least one post-dose imaging evaluation and no major protocol deviations (efficacy analysis set). Dose-expansion data for patients with pancreatic cancer will be published separately. Due to small sample sizes, results in patients with other solid tumours (n=2) are not planned for publication. This ongoing trial is registered with ClinicalTrials.gov, NCT04805307. Findings Between Dec 24, 2020, and Feb 23, 2023, 27 patients were enrolled in the dose-escalation phase (median age 57<middle dot>0 years [IQR 48<middle dot>0-63<middle dot>0]; 14 [52%] male, 13 [48%] female) and 107 patients with gastric or gastro-oesophageal junction cancer in the dose-expansion phase (median age 56<middle dot>0 years [44<middle dot>0-64<middle dot>0]; 57 [53%] male, 50 [47%] female). As of Feb 24, 2024, one dose-limiting toxic effect (grade 3 pancreatitis) occurred at 2<middle dot>2 mg/kg, and the maximum tolerated dose was not reached in the dose-escalation phase. All 27 patients reported at least one treatment-emergent adverse event, most frequently vomiting (19 [70%]), decreased appetite (16 [59%]), proteinuria (16 [59%]), and anaemia (15 [56%]), and five (19%) had drug-related grade 3 or worse treatment-emergent adverse events. In 107 patients, grade 3 or worse treatment-emergent adverse events occurred in 73 (68%) patients and serious adverse events occurred in 54 (50%) patients in dose expansion. The most common grade 3-4 adverse events were neutrophil count decreased (22 [21%]), anaemia (15 [14%]), and vomiting (11 [10%]). One treatment-related death was reported. At median follow-up of 9<middle dot>0 months (IQR 4<middle dot>4-12<middle dot>9), among 113 patients with gastric or gastro-oesophageal junction cancer in the 2<middle dot>2-3<middle dot>0 mg/kg cohort full analysis set across both the dose-escalation and dose-expansion phases, the confirmed objective response rate was 28% (95% CI 20-38; 32 of 113 patients). In the 109 patients included in the efficacy analysis set, the confirmed objective response rate was 29% (95% CI 21-39; 32 of 109 patients). Based on overall safety, activity, and pharmacokinetics of CMG901, 2<middle dot>2 mg/kg was the proposed recommended phase 2 dose. Interpretation CMG901 showed a manageable safety profile and had promising antitumour activity in patients with advanced gastric or gastro-oesophageal junction cancer.<br /> Copyright (c) 2025 Elsevier Ltd. All rights reserved, including those for text and data mining, AI training, and similar technologies.