By Ryan Vlastelica
NEW YORK (Reuters) - Onyx Pharmaceuticals Inc on Sunday confirmed it had rejected an offer from Amgen Inc to buy the company for $120 a share in cash.
The company said that the offer price "significantly undervalued" its prospects, though it was "actively exploring" the potential to combine with another company.
Shares of Onyx closed Friday at $86.82; the offer price represents a premium of about 38 percent from that level.
The Financial Post reported the offer on Friday, sparking a steep jump in Onyx shares in after-hours trading.
Onyx has a market cap of $6.32 billion, according to Thomson Reuters data, while Amgen has a market cap of about $74 billion, based on its Friday closing price of $98.66.
(Editing by Doina Chiacu)