Shares of Protagonist Therapeutics Inc. /zigman2/quotes/205674595/composite PTGX -0.90% soared 87.0% in premarket trading on Monday after the company said the Food and Drug Administration had lifted a clinical hold on clinical trials of rusfertide, its experimental blood cancer treatment. The hold was put into place over concerns of skin tumors from animal research and a deeper examination of four new cancer cases that emerged during a clinical trial. No safety concerns were identified during the hold. The investigational treatment is expected to move forward into a Phase 3 clinical trial for polycythemia vera in the first quarter of next year. SVB Leerink analyst Joseph Schwartz told investors that lifting the clinical hold is a "very welcomed surprise, given the hold was disclosed less than a month ago, and it was unclear how long it would last." Protagonist's stock is down 9.5% so far this year, while the broader S&P 500 /zigman2/quotes/210599714/realtime SPX -1.04% is up 16.9%.