Amgen is rumoured to be planning a higher offer to acquire Onyx Pharmaceuticals, having had an earlier bid of $120 per share rejected by the cancer specialist.

Bloomberg has reported that Amgen is now looking to offer $130 per share, citing a person familiar with the matter. Once its original bid was turned down in June, Onyx said that it was talking to other potential suitors but the news agency's source claims that Amgen's offer is currently the highest bid on the table.

Onyx is best-known for its partnership with Bayer and the liver and kidney cancer drug Nexavar (sorafenib), plus Stivarga (regorafenib) for the treatment of metastatic colorectal cancer and gastrointestinal stromal tumours. Its own therapy for multiple myeloma, Kyprolis (carfilzomib) was approved last year.

Not surprisingly, Bayer has been mentioned as a possible buyer, though the firms were involved in a legal spate over the ownership of Stivarga not so long ago, as has Celgene Corp.