NovaBridge (NBP): CLDN18.2 Drug Population Loses Staining Cutoff

NovaBridge Biosciences (NBP) told investors on 20 August 2026, on its first-half 2026 earnings call and in a 6-K filed the same day, that the FDA has confirmed in writing that its gastroesophageal cancer drug givastomig is eligible for an accelerated approval pathway in first-line treatment — and that the patient population the agency defined requires only that the CLDN18.2 protein be present, with no staining-intensity cutoff attached. NovaBridge is the only company that has disclosed this.

How two numbers on a stain report decide who gets the drug

Gastroesophageal adenocarcinoma grows where the stomach meets the esophagus. CLDN18.2 is a protein normally tucked between the cells lining the stomach; once a cell turns cancerous the protein becomes exposed on the surface, and drugs aimed at it use that protein to find the cancer cell. Whether a patient can take one of these drugs comes down to two numbers on an immunohistochemistry stain report: what share of tumor cells take up the stain, and how strongly they stain.

Vyloy, the approved drug in the same class, sets the bar at 75% or more of tumor cells with moderate-to-strong staining. On that definition, roughly 38% of gastric and gastroesophageal junction patients qualify [3]. The first-line population NovaBridge obtained from the FDA is written only as "CLDN18.2-positive," with no share or intensity qualifier [1][2], and the company enrolls its own trials at "one plus staining and as little as 1% of cells" [1]. Once patient selection turns on whether the protein is there rather than how much of it is there, other developers aiming at the same target have to revisit how narrowly their own trials are enrolling.

Response rates did not fall in the low-expression group, and the company resized the market

NovaBridge stratified the Phase 1b dose-expansion data it released in January 2026: at the 8 mg/kg dose, patients with CLDN18.2 expression at or above 75% had a 76% objective response rate, and patients below 75% had 78% [4]. The low-expression group did not do worse, and on the 20 August call the company listed this as one of three differentiators [1].

The 6-K puts the resized market this way: about 180,000 patients are newly diagnosed with first-line gastroesophageal adenocarcinoma each year across the United States, France, Germany, Italy, Spain, the United Kingdom and Japan, of whom roughly 105,000 are HER2-negative and CLDN18.2-positive [2]. The footnote behind that figure assumes CLDN18.2 positivity of about 70%, and the gap between that 70% and the 38% above is the whole commercial content of the change. The 105,000 is the company's own arithmetic on its own assumption, not a number a regulator or a diagnostics maker has endorsed.

Whoever defines the population defines how big the market is

Sales volume for drugs in this class is set by how the companion diagnostic is read: wherever the label draws the line is how many patients count as treatable. Once the line is drawn on presence rather than expression level, later developers can design Phase 3 trials around a wider population, while programs already built on the narrow definition carry the cost of amending their protocols.

Two boundaries hold. The population the FDA defined is still restricted to PD-L1-positive patients; the company's chief medical officer said on the call that the FDA interactions covered only the PD-L1-positive population and that PD-L1 below 1% was not discussed [1]. And loosening the threshold does not by itself produce efficacy: Elevation Oncology lowered enrollment for its own CLDN18.2 drug to IHC 2+ and at least 20% of cells, saw a 22.2% monotherapy objective response rate, and later terminated the program [5]. The checkable moment is defined — NovaBridge plans to start Phase 3 as early as the fourth quarter of 2026, and the enrollment criteria and primary endpoint it publishes then are the most direct test of whether this change in definition holds [6].

Companies exposed to the same mechanism

• Lepu Biopharma (02157.HK): The CLDN18.2 antibody-drug conjugate held through its joint venture is licensed to AstraZeneca, so its milestone and royalty income rides on how the population is defined and which endpoint a filing runs on.
• Antengene (06996.HK): Its CLDN18.2 drug ATG-022 still has a Phase 3 designed the old way — third line, with enrollment fenced at IHC 2+ and above 20% — making it the most direct place to watch whether such designs get changed.

Sources

[1] Drillr · NovaBridge Biosciences · 2026-08-20 · First-half 2026 earnings call

"Unlike competing approaches limited to high CLDN18.2 expression, Givastomig has demonstrated responses across all expression levels, opening access to a much broader patient population."

[2] US SEC · NovaBridge Biosciences Form 6-K Exhibit 99.1 (first-half 2026 results and pipeline) · 2026-08-20 · Company filing · https://www.sec.gov/Archives/edgar/data/0001778016/000119312526357819/nbp-ex99_1.htm

[3] OncLive · FDA approves the CLDN18.2 companion diagnostic for zolbetuximab (Vyloy) · 2024-10-18 · Industry report · https://www.onclive.com/view/fda-approves-companion-diagnostic-for-zolbetuximab-in-cldn18-2-gastric-gej-cancer

[4] NovaBridge Biosciences press release (via Yahoo Finance) · Givastomig Phase 1b dose-expansion data by expression level · 2026-01-13 · Company press release · https://finance.yahoo.com/news/novabridge-presents-positive-givastomig-dose-120000939.html

[5] Precision Medicine Online · Elevation Oncology terminates CLDN18.2 antibody-drug conjugate EO-3021 and reduces workforce · 2025-03-06 · Industry report · https://www.precisionmedicineonline.com/precision-oncology/elevation-oncology-terminates-cldn182-targeted-adc-reduces-workforce

[6] GlobeNewswire · NovaBridge Biosciences first-half 2026 results release (upcoming givastomig milestones) · 2026-08-20 · Company press release · https://www.globenewswire.com/news-release/2026/08/20/3348212/0/en/novabridge-reports-first-half-2026-financial-results-and-highlights-pipeline-momentum-and-strategic-execution.html

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