Onyx Pharmaceuticals, Inc. (NASDAQ: ONXX ) has said that it has rejected an acquisition offer from Amgen, Inc. (NASDAQ: AMGN ). Amgen was prepared to offer around $120 per share for Onyx, but the board considers this an extremely low offer–it believes that Onyx Pharmaceuticals, Inc. (NASDAQ:ONXX)'s rich drug portfolio can fetch around $140 to $150 per share. Onyx has recently gained prominence for its cancer drug Kyprolis, which received FDA approval last year.