ERBB4 and granular cell tumor: Our previous studies have indicated that GCT tumor cell expresses all four EGFR isoforms (EGFR, ERBB2, ERBB3 and ERBB4) and is able to produce EGFR ligands such as EGF and TGF-α.35 We also found that TGF-α is able to promote GCT tumor cell growth via a TGFα/ERBBs autocrine/paracrine loop in GCT.35 AKT1 is a known critical mediator of the EGFR signaling transduction.