Investors have poured billions into a successor to Merck’s Keytruda, but emerging data dampens hopes for a single blockbuster. Summit Therapeutics, backed by billionaire Bob Duggan, sparked a rally when early results suggested its antibody ivonescimab outlasted Keytruda in a lung‑cancer cohort. The stock surged, lifting the company’s market value above $20 billion, briefly eclipsing Moderna and fueled speculative bets throughout the sector.

Subsequent presentations at the ASCO conference in Chicago showed the drug still lagging behind Keytruda on overall survival, positioning it as a niche competitor rather than a replacement. The dual‑mechanism class—combining checkpoint inhibition with tumor‑vascular blockade—promises incremental market share but requires costly trials. Summit’s valuation now hovers just above $11 billion despite lacking an approved U.S. product, showing difficulty in heavily pre‑treated groups.

Several biotech firms fielding combos signal end of a one‑size‑fits‑all immunotherapy era. Investors must reassess exposure to singular “Keytruda‑killer” narratives and focus on pipelines that can capture defined indications. Summit’s next milestone—regulatory clearance—will likely anchor the company's valuation for the next twelve months. The market will price in any efficacy signals, forcing a sharp re‑rating of biotech stocks tied to this approach.