OPCML is a highly conserved glycosylphosphatidylinositol (GPI) anchoring protein, which belongs to the IgLON family. OPCML inhibits the hallmark phenotypes of a variety of cancers in vitro and exerts a tumor suppressor effect in vivo by downregulating/inactivating a specific spectrum of Receptor Tyrosine Kinases (RTKs), including EphA2, FGFR1, FGFR3, HER2, HER4, and AXL.