** Shares of biotech firm Greenwich LifeSciences GLSI.O rise 6.6% to $17.39 premarket

** Co says U.S. and European regulators approved protocol changes to expand its late-stage study of experimental breast cancer immunotherapy glsi-100

** Trial tests whether glsi-100 can prevent HER2-positive breast cancer, a common type of breast cancer, from returning after surgery and treatment

** Co plans to expand enrollment to as many as 2,000 patients across nearly 200 sites in the U.S. and Europe, with additional countries planned

** Says changes could speed enrollment by allowing more patients to qualify and help generate results sooner

** Preliminary data from an open-label arm showed lower cancer recurrence rates, though the co says results remain early and could change

** As of last close, stock down ~22% YTD