Amgen Inc. plans to acquire Bay Area biotech company Five Prime Therapeutics for $1.9 billion in cash, or $38 per share.

The deal is set to close by the end of the second quarter, the Thousand Oaks pharmaceutical company said.


Five Prime is known for immuno-oncology development, with its lead asset in Phase 3 clinical trials to treat gastric cancer, according to a statement issued by Amgen. Data suggest the drug may be able to treat lung, breast and ovarian cancer too, although there aren’t any official clinical trials in place yet.


Amgen plans to use its acquisition of Five Prime to further its international expansion strategy, as gastric cancer is one of the world’s most common forms of cancer and “particularly prevalent” in Asia, the company said.


In addition to marketing the drug to Japan and other Asia-Pacific markets, Amgen plans to receive a royalty percentage on future net sales of the gastric cancer drug in China, thanks to a pre-existing co-development and commercialization agreement between Five Prime and Shanghai biotech Zai Lab Co.


Five Prime’s pipeline programs complement Amgen’s oncology therapies.


“We look forward to welcoming the Five Prime team to Amgen and working with them to leverage our best-in-class monoclonal antibody manufacturing capabilities to supply additional clinical materials, as well as expanded production quantities, to realize the full potential of bemarituzumab for even more patients around the world,” Robert Bradway, chief executive of Amgen, said in a statement.


“We see tremendous complementarity between the two companies,” added Five Prime Chief Executive Tom Cevik. “Amgen has global reach, world-class resources, and they share our deep passion for science and commitment to patients.”


Shares of Amgen (AMGN) on Thursday closed down $2.03, or less than a percent, to $221.91 on the Nasdaq on a day when the market was down 2.1 percent. Shares of Five Prime Therapeutics (FPRX) closed up $16.74, or 78 percent, to exactly $38 on the Nasdaq.