A bispecific antibody-drug conjugate beat chemotherapy in treated EGFR lung cancer

For non-small-cell lung cancer driven by an EGFR mutation, a targeted tablet such as osimertinib is usually the first treatment, and it works well — until the cancer eventually finds a way around it. What to do next has long meant falling back on platinum-based chemotherapy. A phase 3 trial published in The Lancet on 26 October tested a new kind of drug in that gap [s1].

What the drug is

Izalontamab brengitecan, written iza-bren in the trial report, is a first-in-class bispecific antibody-drug conjugate [s1]. Two features set it apart from ordinary chemotherapy. First, it is bispecific: its antibody component is built to latch onto two different growth-signal receptors on cancer cells at once, EGFR and HER3, rather than one [s1]. Second, it is a conjugate: that antibody carries a chemotherapy payload and delivers it to the cells it binds, aiming to concentrate the toxic effect on the tumour rather than spread it through the whole body [s1].

Targeting EGFR and HER3 together is a deliberate choice. Both are receptors that lung cancers can lean on, and reaching cells that display either one widens the range of tumour the drug can bind. In an antibody-drug conjugate the antibody's main job is delivery — getting the payload to the cancer cell — so the two targets broaden that delivery rather than acting as two separate attacks.

PANKU-Lung01 asked a specific question: once an EGFR-mutated lung cancer has progressed despite a third-generation EGFR tablet, does this bispecific drug delay progression longer than the platinum chemotherapy that would otherwise be used [s1]?

How the trial was built

PANKU-Lung01 was a multicentre, randomised, open-label, phase 3 trial conducted at 73 sites in China, registered as NCT06382116 [s1][s2]. Eligible participants had EGFR-mutated, locally advanced or metastatic non-squamous NSCLC that had progressed after a third-generation EGFR tyrosine kinase inhibitor, and had not yet had chemotherapy for advanced disease [s1]. Of 654 people screened, 222 (34%) were excluded and 432 (66%) were randomly assigned 1:1 — 217 to iza-bren and 215 to chemotherapy; 422 (98%) received treatment and made up the analysis population [s1].

The iza-bren group received the drug at 2.5 mg/kg intravenously on day 1 and day 8 of each three-week cycle [s1]. The control group received pemetrexed plus either carboplatin or cisplatin for four to six cycles, with pemetrexed maintenance allowed for those without progression [s1]. The primary endpoint was progression-free survival, judged by a blinded independent central review panel reading the scans without knowing which treatment a patient was on [s1].

What it found

The primary endpoint favoured iza-bren clearly. Median progression-free survival was 11.1 months (95% CI 9.2–12.7) with the antibody-drug conjugate against 5.7 months (5.5–5.9) with chemotherapy, a hazard ratio for progression or death of 0.40 (95% CI 0.31–0.51; one-sided p<0.0001) [s1]. Median follow-up was 14.6 months in the iza-bren arm and 15.2 months in the chemotherapy arm, so this is the prespecified final progression-free survival analysis rather than an early look [s1].

The trade-off was toxicity. Grade 3 or worse treatment-related adverse events occurred in 170 of 216 patients (79%) on iza-bren versus 128 of 206 (62%) on chemotherapy, predominantly affecting the blood [s1]. Treatment-related side effects led to permanent discontinuation of at least one component of treatment in four patients (2%) in each group, and there was one treatment-related death in each group [s1]. Treatment-related interstitial lung disease — inflammation of the lung that is a known risk with this class of drug — occurred in two patients (1%) on iza-bren and none on chemotherapy [s1].

What is, and is not, established

What PANKU-Lung01 supports is that, in EGFR-mutated non-squamous NSCLC that has progressed after a third-generation EGFR tablet, izalontamab brengitecan nearly doubled progression-free survival compared with standard platinum chemotherapy [s1]. The authors describe it as, to their knowledge, the first phase 3 evidence for a bispecific antibody-drug conjugate, and support it as a potential option in this setting [s1].

The qualifications matter. Overall survival — whether people actually lived longer — was reported only as an interim analysis here, so the most important question is not yet settled [s1]. Severe side effects were more frequent than with chemotherapy, much of the burden falling on the blood, a real cost to weigh against the longer hold on the disease [s1]. The trial was open-label, which is why the blinded central review of scans is the safeguard against biased reading of progression [s1]. It was conducted entirely in China, so how far the results generalise to other populations is not established [s1]. And iza-bren is investigational; these results describe a trial, not an approved treatment [s1].

Red flags: anyone on an antibody-drug conjugate who develops a fever, breathlessness, a new or worsening cough, severe fatigue, or unusual bruising or bleeding should contact their oncology team, as these can signal low blood counts or lung inflammation. This article describes research and is not medical advice. Treatment choices after a targeted tablet fails are for patients and their treating oncologists.