HER2–HER3 blockade in NRG1 fusions: The mechanism changing NSCLC care
Zenocutuzumab gives NRG1 fusion–positive NSCLC a real targeted option: ORR 29%, DOR 12.7 months, PFS 6.8 months in heavily pretreated patients.
The target is HER2–HER3 signaling, not a kinase fusion—making this a biologically distinct driver that requires different therapeutic thinking.
DNA-only NGS may miss NRG1 fusions; RNA-based fusion testing should be built into upfront profiling when tissue allows.
For most oncologists, NRG1 fusions have long existed in the background—a rare genomic footnote signaling aggressive tumor biology with no effective targeted therapy in sight. [] That has since completely changed.
The approval of zenocutuzumab, grounded in data from the eNRGy trial, marks a turning point for this overlooked patient population and forces an urgent question: How do we optimize timely detection of these rare fusion events before the window of opportunity closes? []
Related: IMA histology should trigger RNA sequencing in NSCLC—here’s whyA unique driver that demands a unique approach
NRG1 fusions are not your typical oncogenic rearrangement. Where most targetable fusions—ALK, RET, ROS1—generate chimeric receptor kinases, NRG1 fusions produce chimeric ligands.
The fused protein retains an EGF-like domain that binds directly to HER3, triggering heterodimerization with HER2 and downstream activation of the PI3K–AKT–mTOR proliferation axis. The therapeutic target is the HER2–HER3 signaling handshake, not a mutated receptor. []
Zenocutuzumab was engineered precisely to interrupt that handshake. As a bispecific IgG1 antibody, it docks onto HER2 and simultaneously blocks both HER2–HER3 dimerization and NRG1 ligand binding to HER3, dismantling the fusion protein's mechanism of action at two distinct points of contact. []
What eNRGy showed in NSCLC
Among the 93 evaluable NSCLC patients with measurable disease in the eNRGy trial, zenocutuzumab produced a confirmed objective response in 29%, with a median duration of response of 12.7 months and a median progression-free survival of 6.8 months.
Critically, 87% of patients had received prior systemic therapy, including platinum-based chemotherapy (76%), immunotherapy (56%), and afatinib (9%), making these results a credible reflection of a heavily pretreated, real-world population. []
The historical comparison is sobering. In the largest registry study of NRG1 fusion-positive NSCLC, platinum-based chemotherapy yielded a response rate of just 13%, while single-agent immunotherapy reached only 20%, with a progression-free survival of 5.8 and 3.6 months, respectively. [] Against that benchmark, zenocutuzumab's depth and durability of response represent an outstanding step forward.
The safety profile reinforces the clinical case. Adverse events were predominantly grade 1 or 2—diarrhea, fatigue, and nausea being the most common treatment-related events—and only one patient discontinued therapy due to a treatment-related adverse event. []
The sequencing problem you can't ignore
There is a critical operational challenge embedded in all of this: NRG1 fusions are frequently missed by standard DNA-based sequencing panels. The large intronic regions of NRG1 fall outside the scope of most DNA next-generation sequencing assays, making RNA-based testing essential for reliable detection. []
This demands a deliberate rethinking of testing strategy—thoughtful biopsy planning to maximize sample adequacy, tumor enrichment through microdissection where feasible, and upfront comprehensive profiling that incorporates RNA sequencing alongside DNA from the outset to maximize NRG1 fusion detection.
Related: Bridging NSCLC treatment gaps: ‘The clinical stakes of missing an NRG1 fusion are not abstract’The bottom line
Zenocutuzumab offers the first targeted therapy in NRG1 fusion-positive NSCLC with meaningful, durable activity and a favorable safety profile.
The remaining challenge is one of detection, and the solution starts with a comprehensive testing strategy that incorporates RNA-to-DNA sequencing. Patients with this rare fusion deserve the chance to be found.