Shares of Sorrento Therapeutics Inc. /zigman2/quotes/205669265/composite SRNE -7.24% soared 47% in premarket trading on Friday on heavy volume after the company said it received an offer from an unnamed private equity firm on Thursday. The proposal is for the acquisition of a majority or all of Sorrento's shares for up to $7 per share. Sorrento said its board is currently reviewing the proposal. Last month, the company added two board members: Edgar Lee, then a managing director at Oaktree Capital Management, and Dr. Robin Smith, a physician who also serves on a number of boards, including Celularity Inc. and Seelos Therapeutics /zigman2/quotes/201189599/composite SEEL -4.96% . Sorrento's stock is up 38% over the last 52 weeks. That's compared to the S&P 500 /zigman2/quotes/210599714/realtime SPX -1.84% , which has gained 26%.