Cullinan/Taiho's zipalertinib adds six months of PFS in Phase III EGFR ex20ins trial

Adding zipalertinib to platinum-based chemotherapy extended median progression-free survival (PFS) by six months compared with chemotherapy alone in previously untreated EGFR exon 20 insertion (ex20ins)-mutated non-small cell lung cancer (NSCLC). The drug is being developed by Taiho Pharmaceutical and Cullinan Therapeutics, with the detailed Phase III REZILIENT3 results presented at the International Association for the Study of Lung Cancer's 2026 World Conference on Lung Cancer in Seoul.

The trial enrolled 285 adults with previously untreated, locally advanced or metastatic non-squamous NSCLC harboring EGFR ex20ins mutations. At a pre-planned interim analysis after 122 PFS events, the combination arm (n=140) achieved a median PFS of 14.5 months versus 8.5 months for chemotherapy alone (n=139), yielding a hazard ratio of 0.50 (95% CI 0.34–0.73; P=0.00015). The PFS benefit held in the brain metastases subgroup (HR: 0.38), a clinically relevant finding given that approximately 31% of patients in each arm had brain metastases at baseline. Objective response rate was 65.0% with the combination versus 40.3% with chemotherapy (P<0.0001), with a longer median duration of response (14.2 versus 9.9 months). An interim overall survival analysis at 30% event maturity showed a hazard ratio for death of 0.72 (95% CI 0.42–1.23); follow-up is ongoing.

Grade ≥3 adverse events were more frequent with the combination (87.1% versus 54.4%), driven predominantly by manageable hematologic toxicity (58.6% versus 28.7%). EGFR-related grade ≥3 toxicities were infrequent; rash occurred in 10.7% and diarrhea in 1.4% of patients in the combination arm only. No new safety signals were observed.

Zipalertinib is a covalent, irreversible oral EGFR inhibitor designed to selectively target exon 20 insertion mutants while sparing wild-type EGFR, a property intended to limit the class-effect toxicities that have historically constrained broader EGFR inhibition. The molecule is being developed by Japan-based Taiho Pharmaceutical Co., Ltd. and its subsidiary Taiho Oncology, Inc., in collaboration with Cambridge, Massachusetts-based Cullinan Therapeutics (Nasdaq: CGEM).

The REZILIENT3 data materially strengthen zipalertinib's regulatory position. The FDA accepted an NDA in April 2026 for the second-line setting — patients with ex20ins NSCLC who progressed on or after platinum-based chemotherapy, with or without amivantamab — based on the Phase I/II REZILIENT1 trial, which demonstrated a confirmed objective response rate of 35% in 176 patients. That application carries a PDUFA target action date of February 27, 2027. Taiho and Cullinan said they plan to discuss first-line regulatory submissions with the FDA based on REZILIENT3.

The first-line ex20ins NSCLC space is currently occupied by Johnson & Johnson's Rybrevant (amivantamab), an EGFR/MET bispecific antibody approved in combination with carboplatin and pemetrexed following the PAPILLON trial, which reported a median PFS of 11.4 months versus 6.7 months for chemotherapy. Zipalertinib's 14.5-month median PFS with a chemotherapy backbone compares favorably in absolute terms, though cross-trial comparisons are constrained by differences in patient populations, data maturity, and trial design. Dizal Pharmaceutical's Zegfrovy (sunvozertinib), a second oral ex20ins inhibitor that received FDA accelerated approval in July 2025 in the second-line setting, has also reported positive Phase III data as monotherapy versus chemotherapy in the first-line setting, adding further competitive pressure across both lines.

Cullinan received USD 275 million upfront under its May 2022 deal with Taiho and is eligible for up to USD 100 million upon first-line US regulatory approval of zipalertinib, alongside a 50/50 US profit share.

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