** Shares of drug developer Cogent Biosciences COGT.O rise 128% to $33.25 premarket

** Co says its experimental combo drug, significantly delayed disease progression in patients with an advanced form of stomach cancer in a late-stage study

** COGT tested the drug, bezuclastinib, in combination with Pfizer's PFE.N Sutent in patients with gastrointestinal stromal tumors, who had stopped responding to or could not tolerate imatinib, a standard first-line treatment

** Patients on the combination lived for a median of 16.5 months without their cancer worsening, compared to 9.2 months for those on Sutent alone

** "The positive results with unprecedented effect size and no safety concerns clearly exceed Street expectations by a wide margin," says Guggenheim analyst Michael Schmidt

** Stock up 90% YTD

(Reporting by Kamal Choudhury in Bengaluru)

((Kamal.Choudhury@thomsonreuters.com;))