Sonesitatug vedotin won overall survival in CLARITY-Gastric01 and missed its PFS co-primary — and moved the CLDN18.2 bar to 25%

What AstraZeneca actually disclosed

AstraZeneca published a company release on 27 July 2026, on Businesswire and on its own media centre, reporting positive high-level results from CLARITY-Gastric01 ^[1][2]. The trial is the global Phase III of sonesitatug vedotin (Sone-Ve) — a CLDN18.2-targeting antibody-drug conjugate with a monomethyl auristatin E payload — against investigator's choice of therapy in second and later-line advanced or metastatic gastric, gastroesophageal junction (GEJ) or oesophageal adenocarcinoma ^[1].

The endpoint structure is the whole story, so it is worth stating exactly. CLARITY-Gastric01 carried two primary endpoints: PFS by blinded independent central review in the 2L+ population, and overall survival in the 3L+ population ^[1][3].

• OS in 3L+ — met. Statistically significant and, in AstraZeneca's words, highly clinically meaningful ^[1].
• OS across the whole 2L+ population — met, as a key secondary endpoint, on the same terms ^[1].
• PFS by BICR in 2L+ — not met. "Results showed a trend toward improved PFS in patients treated in the 2nd and later-line setting but did not reach statistical significance" ^[1].

That third line is the caveat, in AstraZeneca's own words. It is an unusual shape: the trial won the survival endpoint and missed the progression endpoint, where PFS is normally the easier of the two to hit and OS the one that carries a label.

What the release does not contain is any efficacy magnitude. No hazard ratio, no median OS or PFS, no confidence interval, no p-value, no ORR, and no safety table beyond the statement that Sone-Ve "was well tolerated" with no new safety signals identified ^[1]. AstraZeneca says the data "will be presented at a forthcoming medical meeting and shared with global regulatory authorities" ^[1]. Anyone modelling this asset is still modelling an unquantified win.

The eligibility criterion is the competitive move

CLARITY-Gastric01 enrolled patients with CLDN18.2 expression on at least 25% of tumour cells, at any staining intensity ^[1]. AstraZeneca's own framing of the result leads with that, not with the survival curve: the data "provide opportunity to expand CLDN18.2 positivity to ≥25% expression, representing approximately 60% of patients in this setting" ^[1].

Set it against the approved comparator. VYLOY (zolbetuximab-clzb) is indicated in first-line HER2-negative gastric/GEJ adenocarcinoma whose tumours are CLDN18.2-positive as determined by an FDA-approved test, where positivity is defined as at least 75% of tumour cells demonstrating moderate to strong membranous CLDN18 immunohistochemical staining ^[5].

Two different bars, and the ADC's is lower on both axes — the fraction of cells and the intensity of the staining. The assays differ too: AstraZeneca states that the CLARITY-Gastric01 efficacy analyses will "provide the basis to evaluate the clinical performance of the Ventana SP455 assay" for identifying eligible patients ^[1], where zolbetuximab's label rests on the VENTANA CLDN18 (43-14A) RxDx assay ^[5].

So the competitive question is not only whether the ADC beats the antibody on outcomes. It is whether the ADC's diagnostic redefines who counts as CLDN18.2-positive at all. AstraZeneca sizes the 2L+ opportunity at roughly 183,500 patients a year across the US, EU, China and Japan with advanced or metastatic CLDN18.2-positive, non-HER2-positive gastric/GEJ cancers ^[1].

The registry record, now confirmed

NCT06346392 is CLARITY-Gastric01: the registry's official title ends "(CLARITY Gastric 01)" ^[3]. Its two primary outcomes are exactly the ones AstraZeneca described — progression-free survival in all randomized participants, and overall survival for 3L+ participants ^[3]. Enrolment closed at 594 participants and the primary completion date of 31 May 2026 is recorded as actual ^[3]. As of the 8 July 2026 update the record is still active but no longer recruiting, with no results posted ^[3].

The design detail the two records add to each other: patients were randomised 1:1:1 in Stage 1 to Sone-Ve monotherapy at 2.2 mg/kg or 1.8 mg/kg every three weeks, or investigator's choice, with Stage 2 continuing at 2.2 mg/kg as the recommended Phase III dose ^[1]. The comparator arms in the registry are ramucirumab plus paclitaxel, paclitaxel, docetaxel, irinotecan, TAS-102 and apatinib ^[3]. The trial ran at 175 centres across 19 countries in North America, Europe, South America and Asia ^[1].

Who is exposed

Open Targets lists exactly one drug at approval stage against CLDN18 (claudin 18, ENSG00000066405): zolbetuximab ^[10]. On that competitive-set view no CLDN18.2 antibody-drug conjugate is approved anywhere — against a field in which more than 20 ADCs have already been approved and hundreds more sit in clinical evaluation ^[14]. Sone-Ve is, per the trial's principal investigator, "the first CLDN18.2-targeted antibody drug conjugate to demonstrate an overall survival benefit in this setting" ^[1].

Part of the regulatory runway is already built. Sone-Ve holds Orphan Drug Designation from the US Food and Drug Administration and from the European Commission for gastric and GEJ cancers, and Breakthrough Designation in China for second-line gastric cancer ^[1].

The sharper signal, though, is what AstraZeneca built around the readout before it landed. NCT07431281 — Phase 3, target enrolment 2,130, recruiting since 3 February 2026 — tests sonesitatug vedotin plus capecitabine with or without rilvegostomig in first-line CLDN18.2-positive, HER2-negative gastric, GEJ and esophageal adenocarcinoma, with primary outcomes of PFS (Cohorts 1 and 2) and OS (Cohort 1) and a primary completion date of 16 August 2029 ^[4]. Its intervention list explicitly includes zolbetuximab, alongside nivolumab, capecitabine, 5-FU, oxaliplatin and leucovorin ^[4].

AstraZeneca opened that first-line trial nearly six months before any 2L+ result was public ^[4]. Whatever the intent behind the design, the front-line CLDN18.2-positive pool is being consumed now.

Around the pivotal: four Phase 2s, none with posted results

Four registered Phase 2 studies list AZD0901 among their interventions, none with posted results:

• NCT07143604 — AZD0901 monotherapy in 2L+ CLDN18.2-expressing gastric/GEJ adenocarcinoma, 33 participants, primary outcome ORR; active but no longer recruiting as of 17 June 2026, primary completion 28 September 2026 ^[6].
• NCT06219941 — AZD0901 as monotherapy and in combination in advanced solid tumours expressing CLDN18.2, 224 participants, indications including gastric, GEJ and biliary tract cancer, partners including 5-FU, leucovorin, irinotecan, nanoliposomal irinotecan and gemcitabine; recruiting as of 12 February 2026, primary completion 11 August 2026 ^[7].
• NCT07069712 (GEMINI-PeriOp GC) — perioperative treatment in locally advanced resectable gastric/GEJ/esophageal adenocarcinoma, 100 participants, interventions including AZD0901, rilvegostomig, trastuzumab deruxtecan, capecitabine, 5-FU and FLOT; primary outcomes AEs/SAEs and pathological complete response; recruiting as of 10 July 2026, primary completion 28 January 2027 ^[8].
• NCT05702229 — open-label multi-drug platform in locally advanced unresectable or metastatic gastric/GEJ adenocarcinoma, 163 participants, interventions including AZD0901, rilvegostomig, volrustomig, FOLFOX and XELOX; primary outcomes ORR and PFS6; recruiting as of 14 May 2026, primary completion 30 November 2027 ^[9].

The target biology supports the breadth: CLDN18.2 is expressed primarily in gastric epithelial cells, where it maintains gastric mucosal barrier integrity, and its aberrant expression is closely associated with initiation, progression and tumour-microenvironment remodelling in gastric cancer ^[12]. The disease itself continues to carry a poor prognosis under a biomarker-fragmented algorithm that begins with microsatellite status ^[13]. Outside the US and EU, an Indian CDSCO expert panel cleared an AstraZeneca protocol amendment for an AZD0901 study, per a Medical Dialogues headline dated 4 May 2025 — headline-level secondary sourcing, not a primary regulatory document ^[15].

What to watch, with dates

The efficacy magnitude. AstraZeneca has committed the data to "a forthcoming medical meeting" and to global regulators, naming neither and giving no date ^[1]. Until a hazard ratio and a median are public, the size of the OS benefit — and how a regulator weighs it against a missed PFS co-primary — cannot be modelled. Watch for NCT06346392 to post results ^[3].

The regulatory filings. No FDA, EMA, NMPA or PMDA submission for Sone-Ve appears in the records reviewed for this briefing. The release says only that the data will be "shared with global regulatory authorities" ^[1]. With Orphan Drug Designation in the US and EU and a Breakthrough Designation in China for exactly this second-line setting ^[1], a China filing is the one with a designation already pointed at it — but nothing in these records fixes a submission date or a review clock, and Prognyx will not manufacture one.

11 August 2026 — primary completion for NCT06219941, the study extending CLDN18.2 targeting into biliary tract cancer ^[7]. 28 September 2026 — primary completion for the 33-patient ORR study NCT07143604 ^[6]. 28 January 2027 — GEMINI-PeriOp GC and its pCR endpoint ^[8]. 30 November 2027 — NCT05702229 ^[9]. 16 August 2029 — the first-line Phase 3 ^[4]. These are registry primary completion dates, not scheduled readouts or regulatory decisions.

The now-what

Option 1 — model the PFS miss, not the OS win. Overall survival is the endpoint that carries a label, and CLARITY-Gastric01 won it twice, in 3L+ and across the whole 2L+ population ^[1]. But a co-primary that missed is the handle a regulator, a payer and a competitor's medical affairs team all reach for. The question to answer internally is what an OS benefit without a significant PFS benefit implies about the mechanism and about post-progression therapy in these arms — and AstraZeneca has published nothing yet that lets anyone answer it ^[1].

Option 2 — re-examine your first-line design now, not after 2029. NCT07431281 is recruiting toward a target enrolment of 2,130 patients, with zolbetuximab in the intervention set and a 16 August 2029 primary completion date ^[4]. The contested resource is front-line CLDN18.2-positive patients between now and then. A competing 1L asset that opens for recruitment in 2027 enters a pool that has already been drawn down for over a year.

Option 3 — the diagnostic is now a documented gap, not an open question. Sone-Ve's trial population was CLDN18.2 on at least 25% of tumour cells at any intensity ^[1]; zolbetuximab's US label requires at least 75% with moderate-to-strong membranous staining ^[5]. Different assays underpin each — Ventana SP455 against VENTANA CLDN18 (43-14A) RxDx ^[1][5]. If your asset's eligibility criterion was written against the zolbetuximab bar, it is now written against a narrower population than the one AstraZeneca intends to claim, and that is a protocol and companion-diagnostic decision sitting upstream of any efficacy comparison.

Verdict: threat upgraded — the caveat is real, but it is not the constraint on AstraZeneca. The PFS miss gives a competitor something to say. The 25% threshold, the OS win in both populations and a 2,130-patient first-line trial already recruiting give AstraZeneca something to file. The window closes on the company's disclosure schedule — a medical meeting it has not named — and not on the 31 May 2026 primary completion date that has already passed ^[1][3].