ASCO Summit: Ivonescimab's China Lung Data Shows Promise, But Global Validation Remains Key

ASCO Summit Reached With China Lung Data but New Climb Begins to Prove Global Benefit

Summit Therapeutics' ivonescimab demonstrated a significant survival benefit in a Chinese lung cancer trial presented at ASCO, yet analysts caution that replicating these results in a broader, global population is crucial for its market potential against established therapies like Keytruda. The Phase 3 HARMONi-6 readout met sky-high efficacy expectations but exposed critical questions about demographic representativeness, follow-up maturity, and whether a China-only win can translate into a credible challenge to Merck's dominant PD-1 franchise in non-small cell lung cancer.

Key Takeaways

• Ivonescimab plus chemotherapy reduced the risk of death by 34% in the China-based HARMONi-6 trial, but BMO Capital Markets flagged the study's "non-representative population of young, Chinese men with lung cancer who had smoked" as a central limitation for extrapolating to Western markets.
• Only 21 months of follow-up data were presented, leaving room for the survival advantage to regress as longer-term data mature — a standard concern in oncology that carries outsized weight for a drug seeking to displace Keytruda.
• BMO declared "King Keytruda's reign continues" after digesting the ASCO presentation, arguing the data provide little insight into ivonescimab's potential benefit in a global population.
• Summit's shares fell just under 4% in pre-market trading as investors priced in the gap between strong China efficacy and uncertain global applicability.
• The ongoing HARMONi-3 trial, with a readout due in the second half of 2026, is the pivotal catalyst that will determine whether ivonescimab can compete outside China.

What Did the HARMONi-6 Trial Results Actually Show?

Summit Therapeutics' Chinese partner Akeso presented Phase 3 results at ASCO from the HARMONi-6 study, which enrolled patients with advanced squamous non-small cell lung cancer in China. The trial compared ivonescimab plus chemotherapy against BeOne's Tevimbra (tislelizumab) plus chemotherapy. Ivonescimab reduced the risk of death by one-third compared to the control arm, a result that met analysts' high expectations and appeared to relieve near-term pressure on Summit's share price heading into the broader HARMONi-3 readout.

But the applause faded quickly. BMO Capital Markets' post-ASCO investor note struck a cautious tone: "Does the totality of the ivonescimab data from HARMONi-6 point to broad efficacy across patient types? Simply put, we do not know." The firm characterized the enrolled population as skewed toward young, Chinese male smokers — a demographic that diverges meaningfully from NSCLC populations in the U.S. and Europe, where patients tend to be older and include more never-smokers and women. The trial's gender balance, at 79% male, further underscored the generalizability challenge.

BMO also flagged a notable finding in older patients: ivonescimab showed little survival difference compared to chemotherapy alone in patients over 65. While BMO noted this could theoretically represent a relative framing advantage — since Keytruda has historically shown diminished efficacy in older cohorts — the data were insufficient to draw that conclusion from HARMONi-6 alone. Follow-up duration remains an additional concern. The study tracked patients for just 21 months, and BMO cautioned that "this limited follow-up leaves room for the treatment survival advantage to regress with time as more patient data become available at longer time points." For a drug aiming to unseat an entrenched standard of care backed by years of mature survival data, immature follow-up is a meaningful commercial liability.

Can Ivonescimab Actually Challenge Keytruda?

The central commercial question hanging over Summit is whether ivonescimab can credibly challenge Merck's Keytruda in first-line NSCLC. Keytruda, a PD-1 inhibitor approved across multiple NSCLC indications, remains the global benchmark supported by years of overall survival data from registrational trials. Ivonescimab's bispecific mechanism — targeting both VEGF and PD-1 — offers a differentiated scientific thesis, but scientific differentiation alone rarely displaces an entrenched standard without head-to-head global data.

In September 2024, ivonescimab outperformed Keytruda in the Phase 3 HARMONi-2 trial in a China-only population. Yet BMO's assessment after ASCO was blunt: "King Keytruda's reign continues." The analysts argued that while the HARMONi-6 results were "good — worthy of a plenary, you be the judge — but provide little insight into the potential benefit of ivonescimab in a global population." For BD teams evaluating Summit's partnership with Akeso, the message is clear: China data alone will not secure a competitive position against Keytruda in the U.S. or EU.

Merck has continued to expand Keytruda's label and real-world evidence base. The drug's entrenched position in treatment guidelines means any challenger must demonstrate at least comparable efficacy in a diverse, global population — ideally with a differentiated safety or dosing profile. Ivonescimab's bispecific approach is mechanistically interesting, but mechanism is not a moat without validation.

Why HARMONi-3 Is the Real Inflection Point

The HARMONi-3 trial is designed to answer the questions HARMONi-6 could not. The Phase 3 study is enrolling a broader, more globally representative NSCLC population, with a readout expected in the second half of 2026. A positive result in a diverse cohort could fundamentally alter Summit's valuation and partnership use, positioning ivonescimab as a credible global competitor. A negative or ambiguous result would likely confine the drug's commercial opportunity to China and select Asian markets.

For business development teams, the HARMONi-6 data serve as both a validation and a warning. They validate the growing importance of Chinese clinical data as an early signal for global drug development — a trend accelerating as Chinese biotechs like Akeso generate increasingly sophisticated Phase 3 datasets. But the results also underscore that China-only data, no matter how strong, is an incomplete asset for global commercialization. Any licensing or co-development discussions involving ivonescimab should be contingent on HARMONi-3 results, with deal structures that reflect the remaining clinical and regulatory risk.

Investors are pricing in the uncertainty. Summit's shares fell just under 4% in pre-market trading following the ASCO presentation, suggesting the market had largely anticipated the survival benefit but remains unconvinced about global applicability. The limited 21-month follow-up also carries practical implications for market access: payers and health technology assessment bodies typically require mature overall survival data before granting favorable reimbursement, and any erosion of the survival advantage over time could weaken ivonescimab's value proposition materially.

Beyond HARMONi-3, watch for Akeso's regulatory filing in China, where approval based on HARMONi-6 is expected, and any signals from Summit about ex-China partnership discussions. The bispecific antibody space is heating up, with multiple VEGF/PD-1 combinations in development, and ivonescimab's first-mover advantage in generating Phase 3 data could prove valuable — if the global data cooperate.

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