Summit Therapeutics PLC (SMMT) experienced a significant after-hours surge of 5.03%, following a day of volatile trading activity driven by mixed reactions to new clinical trial data for its lung cancer drug candidate, ivonescimab.

The biopharmaceutical company presented positive Phase 3 results from the HARMONi-6 trial, showing that ivonescimab, developed with partner Akeso, helped patients with advanced squamous non-small cell lung cancer live an average of 27.9 months. This represented a 15% higher survival rate and a 34% reduction in the risk of death compared to an existing immunotherapy treatment combined with chemotherapy.

Initial pre-market gains were reversed during the intraday session as analysts raised concerns about the drug's efficacy in patients aged 65 and above and the translatability of the China-only trial data to global populations. However, the after-hours rally suggests renewed investor optimism, focusing on the drug's potential to become a first-line treatment that outperforms current standards in a challenging cancer setting.