Results from the global Phase III CLARITY-Gastric01 trial show that sonesitatug vedotin (Sone-Ve), a first-in-class CLDN18.2-targeting antibody-drug conjugate (ADC), delivered a statistically significant and highly clinically meaningful improvement in overall survival (OS) in patients with 2nd and later-line CLDN18.2-positive advanced gastric, gastroesophageal junction (GEJ), or esophageal adenocarcinoma (EAC), representing the first reported Phase III OS benefit demonstrated with an anti-CLDN18.2 ADC in this setting.

Clinical Takeaway

Sone-Ve is the first CLDN18.2-targeted ADC to demonstrate an overall survival benefit in previously treated advanced gastric/GEJ cancers in a Phase III setting. The trial’s OS results were met in both the 3rd and later-line primary endpoint and the 2nd and later-line key secondary endpoint, supporting the potential to broaden the eligible patient population to those with CLDN18.2 expression in ≥25% of tumour cells — encompassing approximately 60% of patients in this setting.

Drug Profile & Mechanism

  • Drug name: Sonesitatug vedotin (Sone-Ve)
  • Drug class: Antibody-drug conjugate (ADC)
  • Target: Claudin 18.2 (CLDN18.2), a tight junction protein aberrantly expressed on the surface of gastric and GEJ tumour cells
  • Payload: Monomethyl auristatin E (MMAE), a potent microtubule-disrupting cytotoxic agent
  • Developer: AstraZeneca (wholly owned ADC asset; first pivotal readout from this portfolio)
  • Regulatory designations:
    • Orphan Drug Designation from the US FDA and European Commission for gastric and GEJ cancers
    • Breakthrough Designation in China for 2nd-line gastric cancer treatment

Target Population

  • Patients with locally advanced or metastatic gastric cancer, GEJ cancer, or oesophageal adenocarcinoma (EAC) with CLDN18.2 expression in ≥25% of tumour cells at any staining intensity
  • Patients receiving treatment in the 2nd and later-line setting
  • Estimated ~183,500 patients per year in the US, EU, China, and Japan are treated in the 2nd and later-line setting for advanced or metastatic CLDN18.2-positive, non-HER2-positive gastric/GEJ cancers
  • Approximately 60% of gastric/GEJ cancers express CLDN18.2 in ≥25% of tumour cells, representing a substantial addressable population
  • Prognosis in this setting is poor: fewer than 20% of patients survive beyond one year, and median survival with 2nd and later-line systemic treatment is approximately 5–9 months

Study Design

  • Trial name: CLARITY-Gastric01
  • Phase: III
  • Design: Randomised, open-label, sponsor-blinded, multicentre, global
  • Setting: 175 centres across 19 countries (North America, Europe, South America, and Asia)
  • Indication: 2nd and later-line treatment of advanced or metastatic gastric cancer, GEJ cancer, or EAC with CLDN18.2 IHC+ expression in ≥25% of tumour cells at any intensity
  • Treatment arms:
    • Stage 1 (dose selection): Patients randomised 1:1:1 to Sone-Ve 2.2 mg/kg Q3W, Sone-Ve 1.8 mg/kg Q3W, or investigator’s choice of therapy (comparator arm)
    • Stage 2: Continued with Sone-Ve 2.2 mg/kg Q3W as the recommended Phase III dose
  • Efficacy analyses will also inform validation of the Ventana SP455 assay for CLDN18.2 patient identification

Endpoints

  • Dual primary endpoints:
    • Overall survival (OS) in patients treated in the 3rd and later-line setting
    • Progression-free survival (PFS) as assessed by blinded independent central review (BICR) in the overall 2nd and later-line population
  • Key secondary endpoint: OS in the overall 2nd and later-line population

Efficacy Outcomes

  • OS — 3rd and later-line (dual primary endpoint): MET — Sone-Ve demonstrated a statistically significant and highly clinically meaningful improvement in OS versus investigator’s choice of therapy
  • OS — 2nd and later-line overall population (key secondary endpoint): MET — A statistically significant and highly clinically meaningful OS improvement was also observed in the broader 2nd and later-line population
  • PFS — 2nd and later-line overall population (dual primary endpoint): NOT MET — Results showed a trend toward improved PFS by BICR, but did not reach statistical significance
  • These results represent the first reported Phase III trial to demonstrate OS benefit with an anti-CLDN18.2 ADC in previously treated gastric/GEJ cancers

Safety

  • Sone-Ve was reported to be well tolerated in CLARITY-Gastric01
  • The safety profile was consistent with the previously established profile of Sone-Ve
  • No new safety signals were identified
  • Full safety data will be presented at a forthcoming medical meeting

Key Clinical Implications

✔ First Phase III OS benefit for a CLDN18.2-targeted ADC: CLARITY-Gastric01 establishes Sone-Ve as a potentially practice-changing option in a setting with historically poor outcomes and limited therapeutic advances.

✔ Broader patient eligibility: The use of a ≥25% CLDN18.2 expression threshold at any staining intensity — rather than higher cut-offs used in prior trials — could extend precision treatment access to approximately 60% of patients with advanced gastric/GEJ cancers.

✔ Companion diagnostics development: Validation of the Ventana SP455 assay for CLDN18.2 detection within the trial framework signals a pathway toward standardised biomarker-driven patient selection in clinical practice.

✔ Regulatory pathway underway: Data are being shared with global regulatory authorities. Combined with existing Orphan Drug Designation (US and EU) and Breakthrough Designation (China), Sone-Ve is positioned for expedited regulatory review across key markets.

✔ Potential chemotherapy alternative: Sone-Ve’s mechanism — targeted CLDN18.2 binding with MMAE-mediated cytotoxicity — offers a rationale for substituting conventional chemotherapy in CLDN18.2-positive patients, potentially improving the therapeutic index in later-line treatment.

Bottom Line

The CLARITY-Gastric01 Phase III trial marks a significant milestone in the treatment of advanced gastric and GEJ cancers. Sonesitatug vedotin (Sone-Ve) is the first CLDN18.2-targeting ADC to achieve an overall survival benefit in the 2nd and later-line setting, meeting both its 3rd-line primary OS endpoint and the broader 2nd and later-line key secondary OS endpoint. Although the PFS co-primary endpoint did not reach statistical significance, the OS signal across multiple analyses is clinically compelling. With its favorable safety profile, broad patient eligibility criteria, and accelerated regulatory designations, Sone-Ve has the potential to redefine precision oncology approaches in CLDN18.2-positive gastric, GEJ, and oesophageal adenocarcinoma. Full data are anticipated at an upcoming medical conference.

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