Biotech giant Amgen Inc. intends to make its oncology pipeline more robust with a $1.9 billion cash acquisition of Five Prime Therapeutics, the company announced March 4.Five Prime, a Bay Area immuno-oncology company, has a promising drug in Phase 3 clinical trials to treat gastric cancer, Amgen said. Data suggest the drug, bemarituzumab, may be able to treat lung, breast and ovarian cancer too, although there aren’t any official clinical trials in place yet.In a conference call with its investors, Thousand Oaks-based Amgen said it anticipates an umbrella trial to see which applications are the most promising. Dr. David Reese, vice president of research and development for Amgen, cited a lung cancer application as a possible next step during the call.Amgen plans to further its international expansion with the deal, particularly in Japan and other Asia-Pacific markets where gastric cancer is a “particularly prevalent” disease. Amgen expects to generate roughly 25 percent of its revenue growth in these markets over the next 10 years.“Gastric cancer is the third most common cause of cancer death worldwide, with over 1 million new cases diagnosed annually,” Reese said during the call. “In Asia in particular, gastric cancer is a significant public health challenge. For context, annually there are nearly as many cases of gastric cancer in China, Japan and Korea as there are all major solid tumors in the United States.”In the U.S., Amgen expects to address gastric cancer in 30,000 patients each year through drugs like bemarituzumab.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, the companies said.“Amgen has global reach, world-class resources and they share our deep passion for science and commitment to patients,” Five Prime Chief Executive Tom Cevik said in a statement. “I have full confidence that Amgen is the right company to work with us to bring our innovative cancer treatments to patients and to achieve our mission to rewrite cancer.”Amgen’s acquisition price is $38 per share. After the acquisition announcement, shares of Five Prime Therapeutics (FPRX) surged 78 percent to close at $38 on the Nasdaq. Amgen shares (AMGN) decreased by about 1 percent to rest at $221.91 the same day, March 4.