The FGFR2 (fibroblast growth factor gene 2, a.k.a. BEK) gene is located on chromosome 10q26.13 and encodes splice variants of the receptor tyrosine kinases FGFR2b and FGFR2c. Amplification of the FGFR2 gene leads to overexpression of the FGFR2 protein and subsequently to signal activation. Additionally, during the amplification process the C-terminal deletion of FGFR2 can occur due to exclusion of the last exon from the FGFR2 amplicon. Both, overexpression and deletion of the last exon result in FGFR2 signaling activation based on constitutive phosphorylation of the FRS2 adaptor molecule. The process of ligand independent FGFR2 signaling leads to a more severe malignant phenotype of these tumors. Moreover, high FGFR2 expression is correlated with poor overall survival (OS) and poor disease-free survival (DFS) rates in breast cancer patients. Consequently, FGFR2 gene amplification detected by Fluorescence in situ Hybridization might be used as a prognostic marker e.g. in breast cancer.