AstraZeneca Sone-Ve Phase 3 Win: First CLDN18.2 ADC to Show Survival Benefit in Gastric Cancer

AstraZeneca (AZN) reported positive results from the Phase 3 CLARITY-Gastric01 trial on July 27, 2026, showing that sonesitatug vedotin (Sone-Ve, AZD0901) delivered a statistically significant and clinically meaningful improvement in overall survival versus investigator’s choice of therapy in patients with CLDN18.2-positive advanced gastric cancer. The drug is the first antibody-drug conjugate targeting CLDN18.2 to demonstrate an overall survival benefit in a Phase 3 trial.

AZN closed at $169.64 on July 25, the last trading day before the announcement. The stock has traded in a tight range near $170 for the past week, anchored by a market capitalization of roughly $263 billion. AstraZeneca is a mega-cap, so a single Phase 3 readout in a mid-sized indication will not move the stock dramatically. But the trial matters for the broader CLDN18.2 competitive picture.

What the trial showed

CLARITY-Gastric01 (NCT06346392) is a randomized, open-label, sponsor-blinded, global Phase 3 trial enrolling patients with locally advanced or metastatic gastric cancer, gastroesophageal junction cancer, or esophageal adenocarcinoma whose tumors expressed CLDN18.2 on at least 25% of cells at any staining intensity. Patients were randomized 1:1:1 in a dose-selection stage to Sone-Ve at 2.2 mg/kg or 1.8 mg/kg every three weeks, or investigator’s choice of therapy.

The trial met its dual primary endpoint of overall survival in the 3rd and later-line setting. It also met a key secondary endpoint of OS in the overall 2nd and later-line population, showing a statistically significant and clinically meaningful improvement.

For the other dual primary endpoint, progression-free survival by blinded independent central review in the 2nd and later-line setting, results showed a trend toward improvement but did not reach statistical significance. OS is the more important endpoint in this setting. Median survival for patients receiving 2nd and later-line systemic treatments in advanced gastric cancer runs just 5 to 9 months, so any statistically significant OS gain is a real clinical advance, not an incremental one.

The safety profile was consistent with the known profile of Sone-Ve, with no new safety signals identified. Sone-Ve uses a monomethyl auristatin E (MMAE) payload, the same payload class used in approved ADCs like Adcetris and Padcev, giving clinicians a familiar safety and efficacy benchmark.

The CLDN18.2 angle

CLDN18.2 is a tight-junction protein expressed in gastric cancers and has become one of the most competitive targets in oncology. The only FDA-approved CLDN18.2-targeted therapy is Astellas’s Vyloy (zolbetuximab-clzb), cleared in October 2024 for first-line gastric and GEJ adenocarcinoma. Vyloy’s label requires CLDN18.2 expression on at least 75% of tumor cells with moderate-to-strong membranous staining, as determined by an FDA-approved companion diagnostic.

Sone-Ve’s trial used a 25% expression threshold at any staining intensity. If that threshold holds through regulatory review, it could expand the treatable population significantly. AstraZeneca estimates that roughly 60% of gastric and GEJ cancers express CLDN18.2 at the 25% or higher level, representing approximately 183,500 annual 2nd and later-line patients across the US, EU, China, and Japan. A broader eligible population is the main commercial differentiator Sone-Ve offers over Vyloy, though the two drugs target different lines of therapy and use different mechanisms (Vyloy is a naked antibody; Sone-Ve is an ADC).

The CLDN18.2 pipeline is crowded. AstraZeneca’s own AZD5863, a CLDN18.2/CD3 T-cell engager bispecific antibody licensed from Harbour Biomed, is in Phase 1. Multiple other companies, including BeiGene, have CLDN18.2 ADCs in development. Sone-Ve’s Phase 3 OS win gives AstraZeneca a head start on the ADC side of that race.

First readout from AZN’s wholly owned ADC portfolio

This is the first registrational readout from AstraZeneca’s wholly owned ADC portfolio. The company’s best-known ADC, Enhertu (trastuzumab deruxtecan), is partnered with Daiichi Sankyo, as is Datroway. Sone-Ve was licensed from KYM Biosciences in March 2023, but AstraZeneca holds full development and commercialization rights. A successful filing and approval would establish that AstraZeneca can develop an ADC independently, not just through the Daiichi partnership.

AstraZeneca said the data will be presented at a forthcoming medical meeting and shared with global regulatory authorities. Sone-Ve already holds Orphan Drug Designation from the FDA and the European Commission for gastric and GEJ cancers, plus Breakthrough Designation in China for 2nd-line gastric cancer. No FDA filing date has been announced yet.

What to watch

The full data presentation will matter. Investors should watch for the hazard ratio and median OS figures, the PFS trend details, and the safety breakdown, particularly the rate of peripheral neuropathy and ocular toxicity, which are class effects of MMAE-based ADCs. Also watch for AstraZeneca’s companion diagnostic strategy around the 25% threshold, since the FDA will need a validated assay to identify eligible patients. For more on AstraZeneca’s broader oncology franchise, see our coverage of the Enhertu plus pertuzumab CHMP opinion and Etcamah’s EU approval in ESR1 breast cancer.

AstraZeneca press release | CancerNetwork coverage | ClinicalTrials.gov NCT06346392