On October 18, 2024, the US Food and Drug Administration (FDA) approved zolbetuximab-clzb (Vyloy, Astellas Pharma US, Inc.) for the first-line treatment of adults with locally advanced unresectable or metastatic human epidermal growth factor receptor 2 (HER2)-negative gastric or gastroesophageal junction (G/GEJ) adenocarcinoma whose tumors are CLDN18.2 positive, as determined by an FDA-approved test. FDA also approved the VENTANA CLDN18 (43-14A) RxDx Assay (Ventana Medical Systems, Inc./Roche Diagnostics) as a companion diagnostic device to identify patients with gastric or GEJ adenocarcinoma who may be eligible for treatment with zolbetuximab.
The recommended zolbetuximab-clzb dosage with fluoropyrimidine- and platinum-containing chemotherapy is 800 mg/m2 intravenously (IV) as the first dose, with subsequent dosages of 600 mg/m2 IV every 3 weeks, or 400 mg/m2 IV every 2 weeks.
Zolbetuximab is a chimeric IgG1 antibody targeting Claudin 18.2 (CLDN18.2) originally developed by Ganymed Pharmaceuticals AG, which was acquired by Astellas. Japan’s Ministry of Health, Labour and Welfare approved VYLOY™ for patients with CLDN18.2-positive, unresectable, advanced or recurrent gastric cancer in March 2024 and zolbetuximab was subsequently approved for untreated CLDN18.2-positive, HER2-negative unresectable advanced G/GEJ adenocarcinoma in the United Kingdom and the European Union in August and September 2024, respectively.
The marketing approvals were based on data from the Phase 3 SPOTLIGHT (NCT03504397) and GLOW clinical trials (NCT03653507). Both were randomized (1:1), double-blind, multicenter trials that included patients with CLDN18.2-positive, HER2-negative, locally advanced unresectable or metastatic G/GEJ adenocarcinoma. The SPOTLIGHT trial included 565 patients randomized to receive either zolbetuximab (800 mg/m2 loading dose administered IV followed by 600 mg/m2 every 3 weeks) plus mFOLFOX6 chemotherapy (283 patients) or placebo plus mFOLFOX6 (282 patients). The GLOW study evaluated zolbetuximab plus capecitabine and oxaliplatin as first-line treatment in 507 patients.
In the SPOTLIGHT study, the median progression-free survival (PFS) was 10.6 months (95% CI: 8.9, 12.5) in the zolbetuximab-clzb/chemotherapy arm and 8.7 months (95% CI: 8.2, 10.3) in the placebo/chemotherapy arm (hazard ratio [HR] 0.751 [95% CI: 0.598, 0.942]; 1-sided p-value=0.0066). Median overall survival (OS) was 18.2 months (95% CI: 16.4, 22.9) and 15.5 months (95% CI: 13.5, 16.5), respectively, (HR 0.750 [95% CI: 0.601, 0.936]; 1-sided p-value=0.0053).
In the GLOW study, the median PFS was 8.2 months (95% CI: 7.5, 8.8) in the zolbetuximab-clzb/chemotherapy arm and 6.8 months (95% CI: 6.1, 8.1) in the placebo/chemotherapy arm (hazard ratio [HR] 0.687 [95% CI: 0.544, 0.866]; 1-sided p-value=0.0007). Median OS was 14.4 months (95% CI: 12.3, 16.5) and 12.2 months (95% CI: 10.3, 13.7), respectively (HR 0.771 [95% CI: 0.615, 0.965]; 1-sided p-value=0.0118).
