AstraZeneca’s Sonesitatug Vedotin Shows Significant Survival Benefits in Phase III Trial for Advanced Gastric Cancer

Global Phase III Trial Achieves Dual Primary Endpoints

The CLARITY-Gastric01 trial, conducted at 175 sites across 19 countries spanning North America, Europe, South America, and Asia, met its dual primary endpoints of progression-free survival (PFS) assessed by blinded independent central review in the second-line and later setting, and overall survival (OS) in the third-line and later treatment population. Sonesitatug vedotin showed a statistically significant and clinically meaningful OS improvement compared to investigator’s choice therapy. Additionally, a key secondary endpoint of OS in the broader second-line and later-line patient group was also met, reinforcing the therapy’s efficacy across treatment lines.

The study enrolled patients with locally advanced or metastatic gastric, gastroesophageal junction, or oesophageal adenocarcinoma cancers expressing CLDN18.2 on at least 25% of tumour cells at any staining intensity. In Stage 1, patients were randomized 1:1:1 to receive sonesitatug vedotin at 2.2 mg/kg, 1.8 mg/kg every three weeks, or investigator’s choice therapy. The 2.2 mg/kg dose was selected for Stage 2 as the recommended Phase III dose. While PFS showed a positive trend in the second-line and later setting, it did not reach statistical significance.

Mechanism and Portfolio Position of Sonesitatug Vedotin

Sonesitatug vedotin is an innovative antibody-drug conjugate targeting CLDN18.2, a protein expressed in the stomach lining and validated as a therapeutic target in gastric and gastrointestinal cancers. The therapy combines an anti-CLDN18.2 monoclonal antibody with a protease-cleavable linker and a cytotoxic payload, monomethyl auristatin E (MMAE), enabling targeted delivery of cytotoxic agents to tumour cells expressing CLDN18.2. AstraZeneca positions Sone-Ve as a potential global first-in-class CLDN18.2-targeting ADC, representing the company’s first pivotal readout from its wholly owned ADC portfolio.

AstraZeneca acquired exclusive global development and commercialization rights to sonesitatug vedotin via a licensing agreement with KYM Biosciences in March 2023. Beyond CLARITY-Gastric01, the company is conducting the CLARITY-Gastric02 Phase III trial evaluating Sone-Ve combined with capecitabine, with or without rilvegostomig, as a first-line treatment for advanced or metastatic gastric, GEJ, and oesophageal adenocarcinoma cancers. In Phase II, Sone-Ve is being tested in multiple combination regimens for advanced solid tumours, including expansion into CLDN18.2-positive pancreatic and biliary tract cancers, underscoring AstraZeneca’s confidence in this therapeutic target across tumour types.

Gastric Cancer Burden and Treatment Challenges Beyond First-Line

Gastric and gastroesophageal junction cancers pose a significant global health challenge. According to the announcement, gastric cancer ranks as the fifth most common cancer worldwide and the fifth leading cause of cancer-related death. Nearly one million new cases were diagnosed in 2024, with approximately 650,000 deaths globally. Incidence is rising in patients under 50 years old in many regions. Most patients are diagnosed at advanced or metastatic stages, where prognosis is poor and treatment options limited, with under 20% surviving beyond one year.

Following progression on first-line therapies, treatment options are scarce and outcomes poor, with median survival ranging from 5 to 9 months for patients receiving second-line and later systemic treatments. This creates a substantial unmet need for effective therapies in these settings. AstraZeneca estimates roughly 183,500 patients annually in the US, EU, China, and Japan receive second-line and later treatments for advanced or metastatic CLDN18.2-positive, non-HER2-positive gastric and GEJ cancers, representing a significant potential market for Sone-Ve pending regulatory approvals.

CLDN18.2 Expression Expands Potential Patient Population

CLDN18.2 is an emerging key therapeutic target in gastric and gastrointestinal cancers. The announcement states that approximately 60% of gastric and GEJ cancers express CLDN18.2 in at least 25% of tumour cells. The CLARITY-Gastric01 trial enrolled patients meeting this threshold, which could broaden the eligible patient population substantially in second-line and later settings. This broad expression contrasts with other gastric cancer biomarkers and suggests Sone-Ve could be prescribed to a large proportion of patients if approved.

Efficacy data from CLARITY-Gastric01 will support evaluation of the Ventana SP455 assay for identifying patients with advanced or metastatic gastric, GEJ, or oesophageal adenocarcinoma expressing CLDN18.2 who may benefit from Sone-Ve. This companion or complementary diagnostic assay could be critical for patient selection and treatment stratification in clinical practice.

Safety and Tolerability Profile Confirmed

Sonesitatug vedotin was well tolerated in the CLARITY-Gastric01 trial, with a safety profile consistent with prior studies. No new safety signals emerged during Phase III, indicating no unexpected adverse events at tested doses. This is important given the often fragile condition of advanced gastric cancer patients who may poorly tolerate highly toxic therapies.

The tolerability profile contrasts with conventional chemotherapy options in second-line and later treatments, which can cause significant toxicity and impact quality of life. AstraZeneca’s leadership has highlighted Sone-Ve’s potential to replace traditional chemotherapy with this targeted ADC to improve patient outcomes. Detailed adverse event data, including severity and discontinuation rates compared to control, will be presented at an upcoming medical conference.

Regulatory Designations and Market Access Strategy

Sonesitatug vedotin has received multiple expedited regulatory designations: Orphan Drug Designation from the US FDA and European Commission for gastric and GEJ cancers, and Breakthrough Therapy Designation in China for second-line gastric cancer treatment. These designations offer benefits like extended market exclusivity, fee reductions, and accelerated review pathways, potentially facilitating faster development and market entry.

AstraZeneca plans to present CLARITY-Gastric01 efficacy and safety data at an upcoming medical meeting and submit these results to global regulatory authorities, initiating formal review processes. The timing of regulatory decisions, approval conditions, and post-approval requirements remain to be determined. Concurrent development in first-line settings through CLARITY-Gastric02 suggests AstraZeneca aims to expand Sone-Ve’s indications and market reach if approved.

AstraZeneca’s Comprehensive Gastrointestinal Cancer Pipeline

AstraZeneca’s portfolio includes approved and investigational therapies targeting gastrointestinal cancers across multiple modalities and disease stages. Approved therapies include Imfinzi (durvalumab), an anti-PD-L1 antibody approved with chemotherapy for biliary tract cancers and in combination regimens for hepatocellular carcinoma and gastric/GEJ cancers, and Enhertu (trastuzumab deruxtecan), a HER2-targeted ADC co-developed with Daiichi Sankyo, approved for HER2-positive advanced gastric cancer.

Additional candidates in development include rilvegostomig, a PD-1/TIGIT bispecific antibody evaluated with chemotherapy and other agents as first-line and adjuvant treatments for gastric and biliary tract cancers. AstraZeneca is also advancing AZD5863, a novel CLDN18.2/CD3 T-cell engager bispecific antibody licensed from Harbour Biomed, currently in Phase I. In 2024, gastrointestinal cancers accounted for around 5 million new cases and 3.3 million deaths globally, highlighting AstraZeneca’s strategic focus on this area.

Clinical Leadership Insights

Rui-Hua Xu, M.D., Ph.D., Professor of Medical Oncology at Sun Yat-Sen University Cancer Center and principal investigator of CLARITY-Gastric01, emphasized the clinical importance of the results. He noted metastatic gastric cancer’s aggressive nature and limited options after first-line progression, and highlighted Sone-Ve as the first CLDN18.2-targeted ADC demonstrating overall survival benefit in this setting. Dr. Xu underscored Sone-Ve’s potential to establish a new precision treatment for a broader CLDN18.2-expressing patient population, affirming the trial’s scientific rigor across 175 centres.

Susan Galbraith, Executive Vice President of Oncology Haematology R&D at AstraZeneca, described the results as transformative, with Sone-Ve having the potential to replace traditional chemotherapy and improve patient outcomes. She highlighted the extensive development programme supporting Sone-Ve’s role as a key medicine for CLDN18.2-positive cancers. These statements reflect corporate optimism, with regulatory approval and clinical adoption contingent on future developments.

Milestone for AstraZeneca’s ADC Portfolio

CLARITY-Gastric01 is AstraZeneca’s first Phase III trial demonstrating overall survival benefit with an anti-CLDN18.2 ADC in second-line and later gastric cancer treatment, marking the first pivotal readout from its wholly owned ADC portfolio. This milestone validates AstraZeneca’s ADC platform and may boost confidence in other pipeline ADC candidates.

Unlike some oncology assets developed with partners such as Daiichi Sankyo (Enhertu) or MSD (Lynparza), AstraZeneca’s fully owned ADC portfolio showcases its internal capabilities in ADC innovation. This success could strengthen the company’s position in the growing ADC therapeutic space and influence investor sentiment positively.

Upcoming Data Presentation and Regulatory Steps

AstraZeneca confirmed that detailed efficacy, safety, and pharmacokinetic data from CLARITY-Gastric01 will be presented at a forthcoming medical conference, though specifics were not disclosed. Presentation at major oncology meetings such as ASCO, ESMO, or AACR would provide broad expert review and visibility. Subsequent peer-reviewed publications are expected to further validate findings.

The company will share these data with global regulatory bodies, initiating formal review processes. Timing of submissions, targeted indications, and regulatory pathways (accelerated or standard) remain to be announced. The ongoing CLARITY-Gastric02 trial in first-line therapy suggests AstraZeneca aims for multi-line approvals, potentially expanding Sone-Ve’s market scope.