Summit Therapeutics Inc. (NASDAQ:SMMT), on Sunday, revealed the updated overall survival (OS) results from the global Phase 3 HARMONi trial of ivonescimab at the 2025 World Conference on Lung Cancer (WCLC).
The trial included patients with epidermal growth factor receptor (EGFR)-mutated, locally advanced or metastatic non-squamous non-small cell lung cancer (NSCLC) who have progressed after treatment with a 3rd generation EGFR tyrosine kinase inhibitor (TKI).
Ivonescimab is considered a rival to Merck & Co. Inc.’s (NYSE:MRK) multi-billion dollar cancer drug Keytruda (pembrolizumab).
The stock is trading lower as ivonescimab showed that longer-term follow-up of Western (North America and Europe) patients showed an improving, favorable trend in overall survival, yielding a hazard ratio (HR) of 0.78 and a nominal p-value of 0.0332, but lower than that of Chinese patients.
As previously disclosed, ivonescimab in combination with chemotherapy showed a positive trend in overall survival in the primary analysis without achieving a statistically significant benefit with a hazard ratio of 0.79 (p=0.057). The statistical analysis plan for the study required a p-value of 0.0448 to achieve statistical significance.
Median overall survival was 16.8 months for ivonescimab plus chemotherapy versus 14.0 months for placebo plus chemotherapy.
At the time of the primary analysis, the median follow-up time for Western patients was 9.2 months, which was less than the median overall survival at the time of the primary analysis.
In September 2025, an additional analysis included longer-term follow-up of Western patients (median follow-up time of Western patients of 13.7 months). Data showed a hazard ratio consistent with the primary analysis was observed with an improved nominal p-value (HR=0.78; nominal p=0.0332).
Median overall survival for this analysis remained the same in both arms from the primary analysis.
Median overall survival in Western patients receiving ivonescimab was 17.0 months compared to 14.0 months for those receiving placebo (HR=0.84); median overall survival in North American patients, specifically, had not yet been reached in the ivonescimab arm compared to 14.0 months in the placebo arm (HR=0.70).
Median progression-free survival (PFS) for ivonescimab vs. placebo plus chemotherapy was 6.8 months vs. 4.4 months, respectively.
In a longer-term follow-up of PFS, ivonescimab plus chemotherapy demonstrated a consistent, clinically meaningful improvement in PFS with an observed HR of 0.57.
However, investors are reacting as the risk of tumor progression (PFS) fell by 45% (HR of 0.55) for participants from China treated with ivonescimab and chemotherapy compared to chemotherapy and a placebo.
For participants from Western countries, the risk of tumor progression was reduced by 33% (HR of 0.67).
Overall response rates were higher in the ivonescimab arm (45%) vs. the placebo arm (34%); median duration of response was longer in those patients administered ivonescimab plus chemotherapy (7.6 months) compared to those receiving placebo and chemotherapy (4.2 months).
Ivonescimab demonstrated a favorable safety and tolerability profile, with no new safety signals identified.
Price Action: SMMT stock is trading lower by 18.17% to $21.26 premarket at last check Monday.
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