Princeton, New Jersey, Tokyo, Japan & Cambridge, Massachusetts, August 12, 2026
Taiho Oncology, Taiho Pharmaceutical, and Cullinan Therapeutics announced positive topline results from the planned interim analysis of the global Phase 3 REZILIENT3 clinical trial, evaluating zipalertinib plus platinum-based chemotherapy as a first-line treatment for adults with previously untreated, locally advanced or metastatic non-small cell lung cancer (NSCLC) harboring EGFR exon 20 insertion mutations. The study met its primary endpoint of progression-free survival (PFS), demonstrating a statistically significant and clinically meaningful improvement for the zipalertinib-containing regimen compared with chemotherapy alone.
REZILIENT3 Meets Primary Progression-Free Survival Endpoint
The REZILIENT3 trial is a multicenter, randomized, controlled, open-label global Phase 3 study that enrolled 285 adults with previously untreated, locally advanced or metastatic non-squamous NSCLC carrying EGFR exon 20 insertion (ex20ins) mutations. The primary objective is to compare PFS between patients receiving zipalertinib plus chemotherapy and those receiving chemotherapy alone. At the planned interim analysis, the study demonstrated a statistically significant and clinically meaningful improvement in PFS in the zipalertinib treatment arm. The observed safety profile was reported as manageable. Based on the interim findings, the Independent Data Monitoring Committee recommended that the study be unblinded, while the trial will continue to monitor efficacy and safety. The positive interim analysis represents an important milestone for the development of zipalertinib in the first-line treatment setting. The companies plan to submit the complete REZILIENT3 results for presentation at an upcoming international medical conference. Following discussions with the U.S. Food and Drug Administration (FDA), Taiho Oncology, Taiho Pharmaceutical and Cullinan Therapeutics intend to pursue regulatory approval for the combination regimen in the first-line setting.
Zipalertinib Targets EGFR Exon 20 Mutations
Zipalertinib, also known by the development codes CLN-081/TAS6417, is an orally available small molecule designed to target activating mutations in the epidermal growth factor receptor (EGFR). The investigational therapy was specifically developed to inhibit EGFR variants containing exon 20 insertion mutations and is being studied as a next-generation irreversible EGFR inhibitor for genetically defined patients with NSCLC. Zipalertinib remains investigational and has not been approved by any health authority. EGFR exon 20 insertion mutations represent a distinct molecular subset of NSCLC. The companies report that these mutations occur in up to approximately 4% of NSCLC cases globally, while EGFR mutations overall are present in approximately 16% of NSCLC cases in the United States, with exon 20 insertions accounting for a proportion of those mutations. The development of targeted therapies for this genetically defined population represents an important area of precision oncology research.
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Regulatory Pathway Advances for First-Line Treatment
The REZILIENT3 results strengthen the clinical development program for zipalertinib in EGFR exon 20 insertion-positive NSCLC and provide a potential pathway toward expanding treatment options in the first-line setting. Taiho Oncology, Taiho Pharmaceutical and Cullinan Therapeutics are collaborating on the development of zipalertinib in the United States, with Taiho’s proprietary drug discovery technology supporting the compound’s development. The companies are continuing to evaluate zipalertinib across its clinical development program while preparing for future regulatory interactions. The next major milestone will be the presentation of full REZILIENT3 clinical results, which will provide additional information on the magnitude and durability of the PFS benefit, as well as safety findings. The companies have stated that regulatory approval plans for the first-line combination regimen will be pursued following discussions with the FDA. The positive Phase 3 interim results highlight continued progress in precision oncology and biomarker-driven drug development, particularly for patients with EGFR exon 20 insertion-positive NSCLC. If subsequent analyses and regulatory reviews support the findings, zipalertinib combined with chemotherapy could potentially provide a new first-line treatment approach for this molecularly defined patient population.
Source: Taiho Oncology, Taiho Pharmaceutical, Cullinan Therapeutics press release
