Five Prime's lead asset is bemarituzumab, an antifibroblast growth factor (FGF)/fibroblast growth factor receptor splice variant 2b (FGFR2b) antibody. The candidate targets FGFR2b, which is found to be overexpressed in approximately 30% of patients with nonhuman epidermal growth factor receptor 2 (non-HER2) positive gastric cancer, as well as other solid tumors. Results from a phase II clinical trial in advanced gastric or gastroesophageal junction cancer demonstrated clinically meaningful improvements in patients who received the treatment.

The acquisition of Five Prime also supports Amgen's strategy of expanding its presence in the Asia-Pacific region, where gastric cancer is particularly prevalent.

As part of the transaction, Amgen will receive a royalty percentage on future net sales in China ranging from the high teens to the low twenties from a preexisting co-development and commercialization agreement between Five Prime and Zai Lab.

The transaction is expected to close by the end of the second quarter of 2021. Under the agreement, Amgen will commence a tender offer to acquire all of the outstanding shares of Five Prime's common stock for $38 per share in cash.