RecruitingPhase 1Drug trialSitagliptin in Recurrent/Progressive Grade 4 GliomaSitagliptin, when combined with standard-of-care drug bevacizumab, is being tested to 1) find out if it is effective at treating gliomas that have returned or progressed after treatment, and 2) find out what the highest dose of sitagliptin is appropriate to give when combined with bevacizumab.