Amgen Inc struck a deal to buy Onyx Pharmaceuticals Inc for more than $10 billion on Sunday, ending a two- month-long auction for the cancer drug maker.

Amgen said it will pay $125 per share for Onyx, a 4.2 percent increase from the $120 a share it offered in June. Onyx said that bid significantly undervalued the company and put itself up for sale.

The acquisition represents the fifth-largest biotechnology deal in history and gives Amgen full rights to Kyprolis, the new multiple myeloma drug that analysts expect to reach annual peak sales in excess of $2 billion.

Amgen will also gain a revenue stream from the liver and kidney cancer drug Nexavar that Onyx shares with Bayer AG , as well as royalty payments on Bayer's much newer colon cancer drug, Stivarga, and potential future royalties on an experimental breast cancer drug being developed by Pfizer Inc .

It is Amgen's biggest deal since its $16 billion acquisition of Immunex in 2001 that gave it the rheumatoid arthritis drug Enbrel, which is one of Amgen's biggest-selling products.

It is also by far the biggest deal under CEO Bob Bradway, who assumed the top spot in May 2012. He has done a handful of much smaller deals, the biggest to date being a $1.16 billion acquisition of Micromet.

Onyx shares closed at $116.96 on Friday.

(Reporting by Michael Erman in New York; editing by Matthew Lewis)