FAM59A, also known as GAREM, was initially identified through a mass spectroscoptic method that measures different phosphotyrosine states of proteins in response to different cell stimuli. FAM59A is a downstream molecule in the EGF signaling pathway that is tyrosine-phosphorylated, and this phosphorylation is needed for the binding of Grb2, an adaptor protein crucial to the transduction of growth signals from the plasma membrane to the nucleus. ERK activation in response to EGF stimulation is regulated by FAM59A in COS-7 and HeLa cells, and the overexpression of FAM59A stimulated cell proliferation and colony formation in soft agar, suggesting that FAM59A might be a critical protein with roles in ligand-mediated signaling pathway of the EGF receptor and the tumorigenesis of cells.