Shares in Onyx Pharmaceuticals shot up over 20% following reports that the US biotech is exploring strategic alternatives, including a sale.

Bloomberg reported that Onyx is working with Centerview Partners to review its options, citing two unnamed people with knowledge of the matter. The South San Francisco-based company is making no comment on the rumours.

However, it is clear that Onyx' options have widened since last month when it settled a long-running battle with partner Bayer over rights concerning regorafenib, an oral multikinase inhibitor like the two firms' big-selling liver and kidney cancer drug Nexavar (sorafenib).

In May 2009, Onyx sued over the rights to regorafenib, claiming it is a variant of Nexavar while Bayer has always insisted that the former substance is not covered by the collaboration the companies signed way back in 1994. However, a deal has now been reached, which relieves Onyx from any future development costs for regorafenib, and legal proceedings have been dropped.

Another settlement revealed that in the event of a change of control or acquisition of Onyx, the current profit-sharing, co-development and US co-promotion of Nexavar will be preserved, making the firm more attractive for a takeover.

However, observers believe any deals are some way off. The US Food and Drug Administration is due to decide soon whether to accept Onyx’s filing for accelerated approval of carfilzomib, a multiple myeloma drug and Howard Liang, an analyst at Leerink Swann, told Bloomberg “I would think that any potential acquirer would want to see the outcome of the carfilzomib regulatory review. We are only a few months away.”