FPA144, a humanized monoclonal antibody for both FGFR2-amplified and nonamplified, FGFR2b-overexpressing gastric cancer patients.

e15074 Background: Amplification of the Fibroblast Growth Factor Receptor 2 (FGFR2) gene is reported in ~5% of gastric cancer patients and leads to the specific overexpression of the FGFR2b isoform of the receptor. Five Prime Therapeutics has developed an FGFR2b-specific antibody, FPA144, for treating gastric cancer patients with FGFR2 amplification. We are also investigating the utility of FPA144 in patients with FGFR2b overexpression that lack FGFR2 gene amplification. Results: We developed an FGFR2b-specific antibody for immunohistochemistry (IHC). In a cohort of 186 gastric cancer samples from mostly Asian and Eastern European patients, 6.7% of the samples had FGFR2 amplification as measured by fluorescent in situ hybridization, consistent with published reports. Using our proprietary antibody and IHC methods, we identified an additional 10% of cases with FGFR2b protein overexpression in the absence of FGFR2amplification. These data suggest that as many as 17% of gastric cancer patients may benefit fr...