Amgen will acquire San Francisco, Calif.-based Onyx Pharmaceuticals, purchasing all of the outstanding shares of Onyx for $125 per share in cash, for a total purchase price of $10.4 billion, or $9.7 billion net of estimated Onyx cash. The boards of both companies have approved the transaction.

Onyx is a global biopharmaceutical company developing and commercializing innovative therapies for cancer. Onyx has a multiple myeloma franchise, with Kyprolis (carfilzomib) for Injection already approved in the U.S. Onyx also has three partnered oncology assets: Nexavar (sorafenib) tablets (an Onyx and Bayer HealthCare Pharmaceuticals compound), Stivarga (regorafenib) tablets (a Bayer compound) and palbociclib (a Pfizer compound), plus multiple oncology compounds in various stages of clinical development.

Amgen will launch a tender offer and expects to close at the beginning of the fourth quarter, subject to customary closing conditions, including regulatory clearance.

"We believe that Amgen is ideally suited to realize the full potential of Onyx's portfolio and pipeline for the benefit of physicians and patients," said Robert A. Bradway, chairman and chief executive officer at Amgen. "Our acquisition of Onyx follows a thorough due diligence process and is fully consistent with our strategy of advancing innovative medicines that address serious unmet medical needs. We expect this acquisition will accelerate growth and enhance value for Amgen shareholders.

"Amgen has a unique opportunity to add value to Kyprolis, a product which is at an early and promising stage of its launch," said Bradway.

Onyx holds global rights to Kyprolis, excluding Japan. Kyprolis has an orphan drug designation in the U.S. with exclusivity until July 2019, and patents in the U.S. that extend until at least 2025.

Amgen intends to leverage its oncology capabilities and experience to support Onyx's clinical development programs and maximize Kyprolis' potential in the U.S. and the rest of the world.

The acquisition also adds to Amgen's late-stage pipeline, which includes nine products for which registration-enabling data are anticipated by 2016. Four of these are first-in-class oncology products.

In addition to accelerating Amgen's revenue growth, the acquisition is expected to be accretive to Amgen's adjusted net income in 2015.

"After a careful and thorough evaluation process, our board of directors has determined that the all-cash transaction with Amgen maximizes value for our stockholders and expands the potential of our commercial medicines and clinical pipeline to reach more patients globally," said Dr. Tony Coles, chairman and chief executive officer of Onyx.