THOUSAND OAKS and SOUTH SAN FRANCISCO, Calif. — Amgen plans to acquire oncology specialist Onyx Pharmaceuticals Inc. in a deal valued at $10.4 billion overall.

Under the acquisition agreement, announced Sunday evening, Amgen will purchase all of the outstanding shares of Onyx at $125 per share in cash. Net of estimated Onyx cash, the purchase price is $9.7 billion.

Amgen said it will effect the transaction through a tender offer and expects to close the deal at the start the fourth quarter, pending regulatory clearance and customary closing conditions.

Onyx has a growing multiple myeloma franchise, with Kyprolis for Injection (carfilzomib) already approved in the United States. In addition, Onyx has three partnered oncology assets: Nexavar (sorafenib) tablets (an Onyx and Bayer HealthCare Pharmaceuticals Inc. compound), Stivarga (regorafenib) tablets (a Bayer compound), and palbociclib (a Pfizer Inc. compound). Onyx, too, has multiple oncology compounds in various stages of clinical development.

"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," stated Robert 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.

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

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

Amgen said it will benefit from the global rights to Onyx’s innovative oncology portfolio and pipeline and that it aims to leverage its oncology capabilities and experience to support Onyx’s clinical development programs and boost Kyprolis’ potential worldwide.

The acquisition of Onyx also adds to Amgen’s robust late-stage pipeline, according to the company. The pipeline includes nine innovative products for which registration-enabling data are anticipated by 2016. Four of these are first-in class oncology products. Onyx’s pipeline also complements Amgen’s growing oncology portfolio, the company said.

"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," commented Tony Coles, chairman and CEO of Onyx.

"We are pleased to have reached this agreement with Amgen, a company that shares Onyx’s vision for innovation on behalf of patients," he added.