On September 23, Summit Therapeutics PLC fell 5.03% in regular trading, trading at approximately $16.26 per share, with turnover of $34.73 million.

On the news front, despite the company's core drug candidate ivonescimab generating a string of positive clinical readouts at major international conferences including the World Conference on Lung Cancer and upcoming ESMO presentations, market focus has shifted decisively toward FDA regulatory uncertainty. The key concern centers on the HARMONi global Phase III study, whose primary overall survival analysis did not achieve statistical significance. The FDA has previously indicated that statistically significant OS benefit is required for this indication, and progression-free survival data alone may not be sufficient to support a marketing approval.

This regulatory overhang persists even as ivonescimab demonstrated compelling efficacy in multiple China-based trials, including a 27% reduction in the risk of death versus pembrolizumab in HARMONi-2 and statistically significant OS superiority over durvalumab in the HARMONi-GI1 biliary tract cancer trial. Earlier, H.C. Wainwright downgraded the stock to Neutral and removed its price target, citing competitive pressure from Merck's ADC pipeline. Summit currently has no marketed products and reported EBITDA losses of $1.22 billion over the trailing twelve months.

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