** Shares of drug developer Summit Therapeutics SMMT.O fall 9.7% to $23.66 premarket

** Co says its experimental lung cancer therapy ivonescimab in combination with chemotherapy showed a positive trend in overall survival, but "without achieving a statistically significant benefit" in a global late-stage trial

** However, co says the therapy showed meaningful improvement in progression free survival or the time patients live without their disease progressing

** Co plans to file for marketing approval for ivonescimab, but says the "FDA noted that a statistically significant overall survival benefit is necessary to support marketing authorization," which will weigh into its considerations regarding the timing of filing its US application

** SMMT is testing ivonescimab to treat patients with a type of lung cancer who have progressed after prior treatment

** There were no new safety signals noted in the late-stage study, co says

** Up to last close, stock up 46.9% YTD

(Reporting by Sneha S K)

((Sneha.SK@thomsonreuters.com))