 Shares of Sierra Oncology Inc. SRRA, 3.10 soared 37.3 in premarket trading on Wednesday after GlaxoSmithKline GSK, 0.11 GSK, 0.63 said it would buy the company for 1.9 billion. Sierra is developing treatments for rare types of cancer, including myelofibrosis, and announced in January that momelotinib met the primary and secondary endpoints in a Phase 3 clinical trial evaluating the experimental therapy as a treatment for myelofibrosis. 