FGFR3 is one of 4 high affinity tyrosine kinase receptors for the fibroblast growth factor family of ligands. On ligand stimulation, FGFR3 undergoes dimerization and tyrosine autophosphorylation, resulting in cell proliferation or differentiation, depending on the cell context, through the mitogen-activated protein kinase (MAPK) and phospholipase Cγ signal transduction pathways. Some FGFR3 mutations are believed to result in ligand-independent activation of the receptor. Somatic mutations of FGFR3 gene are not reported in thymic tumors. However, in some cases, the possibility of FGFR3 variants being germline can not be excluded. Clinical correlation is recommended.