Shares of CymaBay Therapeutics Inc. CBAY gained 23% premarket on Thursday after the company released positive results from a late-stage study of seladelpar, its investigational treatment for the rare chronic liver disease primary biliary cholangitis. About 62% of patients treated with seladelpar met the study’s primary endpoint related to serum alkaline phosphatase and bilirubin, compared with 20% of those on placebo, CymaBay said in a release. The study also met key secondary endpoints, including a significant reduction of pruritis, or itching that is a common early symptom of the disease, CymaBay said. The trial data…