An investigational antibody-drug conjugate built to engage two targets at once has produced enough early evidence to settle on the dose that will be carried into a registrational Phase III lung cancer study. The therapy, known as iza-bren, is an EGFR x HER3 antibody-drug conjugate, and investigators have selected 2.5 mg/kg as the recommended Phase III dose for patients with previously treated, EGFR-mutated non-small cell lung cancer (NSCLC).
The findings come from the randomized dose-expansion cohort of a global Phase I study and will be presented at the International Association for the Study of Lung Cancer (IASLC) 2026 World Conference on Lung Cancer in Seoul, Republic of Korea. According to the researchers, clinical activity increased as dose levels rose, and the balance of efficacy and tolerability at 2.5 mg/kg supported advancing that regimen into the global Phase III IZABRIGHT-Lung01 registrational trial.
Efficacy at the Recommended Phase III Dose
At the 2.5 mg/kg dose, the trial recorded a set of efficacy signals that the investigators describe as promising for a patient group that has already been through standard therapy:
- Objective response rate of 33.3%
- Confirmed objective response rate of 29.6%
- Median progression-free survival of 6.9 months
The confirmed objective response rate is the more conservative of the two response measures, counting only responses that held up on subsequent imaging. Median progression-free survival of 6.9 months describes how long, in the middle of the study population, patients lived without their disease advancing. Together, the numbers gave the study team the rationale it needed to stop testing several dose levels and concentrate on a single regimen for late-stage development.
A Heavily Pretreated Population
The dose-expansion cohort was not made up of newly diagnosed patients. Every participant had already progressed on a third-generation EGFR inhibitor, the class of targeted drugs that anchors treatment for EGFR-mutated lung cancer. Nearly two-thirds of the enrolled patients had also received platinum-based chemotherapy, meaning most had cycled through both targeted therapy and conventional cytotoxic treatment before receiving the investigational conjugate.
That history matters when interpreting a 33.3% response rate. Progression on a third-generation EGFR inhibitor, and progression after platinum chemotherapy, are exactly the situations in which new options are needed most, and they are also the settings in which experimental agents most often struggle to produce durable benefit. The trial's design, which escalated through dose levels in a randomized fashion rather than reporting a single-dose snapshot, was intended to identify whether higher doses bought more activity — and the data indicated that they did.
Safety and the Role of G-CSF Prophylaxis
The safety picture was reported as manageable. No treatment-related deaths occurred in the cohort, and only one patient discontinued treatment because of a treatment-related adverse event. The investigators also reported that mandatory primary G-CSF prophylaxis was associated with an improved hematologic safety profile compared with previously reported experience with the agent.
G-CSF, or granulocyte colony-stimulating factor, is given to support the production of white blood cells, and it is commonly used alongside cancer therapies that suppress bone marrow. Antibody-drug conjugates frequently carry payloads that can affect blood counts, so making G-CSF support a required part of the regimen — rather than a reaction to falling counts — appears to have shifted the toxicity profile in a favorable direction. That finding is likely to matter for how the regimen is administered in the Phase III setting, where consistent, protocol-defined supportive care can determine whether a therapy is practical across a broad treatment landscape or limited to specialized centers.
Why Targeting Both EGFR and HER3
The "x" in EGFR x HER3 denotes a therapy designed to engage two distinct targets with a single agent. EGFR is the well-established driver in EGFR-mutated NSCLC, and third-generation inhibitors against it have become standard treatment. HER3 is a related receptor that researchers have pursued as a way to broaden coverage and complicate a tumor's ability to escape a single-target drug.
Antibody-drug conjugates add a second layer to that strategy by pairing tumor-targeting antibodies with a cytotoxic payload, aiming to deliver cell-killing chemotherapy preferentially to cells that display the target. Whether the dual-target design translates into a durable advantage over existing options is precisely what the Phase III program is meant to determine; the Phase I data establish only that the approach is active and tolerable enough to test at scale.
From Phase I to IZABRIGHT-Lung01
The next step is IZABRIGHT-Lung01, described as a global Phase III registrational study. Registrational trials are designed to generate the evidence regulators require to consider approval, which means the endpoints, patient population, and statistical plan will be more demanding than those of the dose-expansion cohort that produced these results.
"These findings support continued development of iza-bren and provide the rationale for advancing the 2.5 mg/kg regimen into the global phase 3 IZABRIGHT-Lung01 trial for patients with previously treated EGFR-mutated NSCLC," said Alexander Spira, M.D., of NEXT Oncology Virginia and Virginia Cancer Specialists in Fairfax, Virginia.
What the Data Do Not Yet Show
Several questions remain open. The results are being presented at a scientific conference and derive from a dose-expansion cohort, so they reflect a comparatively limited, non-registrational experience rather than the randomized comparison that would establish superiority or non-inferiority against an existing standard of care. The durability of responses, how the regimen performs across molecular subgroups of EGFR-mutated disease, and whether the hematologic benefit seen with mandatory G-CSF prophylaxis holds up under broader use are all matters the Phase III trial is positioned to address.
For now, the headline is a dose decision: 2.5 mg/kg moves forward, backed by response and progression-free survival figures that investigators consider encouraging in a population with limited remaining options, and by a safety profile that produced no treatment-related deaths in the reported cohort.
This article is based on reporting by Medical Xpress. Read the original article.
Originally published on medicalxpress.com
