Corbus Pharmaceutical Holdings Inc. /zigman2/quotes/201549545/composite CRBP -0.27% shares surged 21.4% in premarket trade on Thursday after the company reported positive results from a phase 2 trial of its autoimmune disease drug. The drug, anabasum, is intended for the rare inflammatory condition dermatomyositis, which is associated with an itchy and painful rash and progressive muscle weakness, according to the Mayo Clinic. In the clinical trial, which enrolled 22 adults and lasted 16 weeks, the drug outperformed the placebo in the primary efficacy outcome and in multiple secondary efficacy outcomes, the company said. There were also no signs of safety issues, Corbus said. Currently, "we have little to offer patients with moderate to severe disease activity except immunosuppressive therapies with often limited efficacy and significant side effects," said Dr. Victoria Werth, a principal investigator in the study and a professor of dermatology at the Hospital of the University of Pennsylvania. Corbus Pharma shares have surged 6.9% over the last three months to $7.00 per share, compared with a 3.5% rise in the S&P 500 /zigman2/quotes/210599714/realtime SPX +0.48% .