(a) Summary of the three reactions (ligand binding, dimerization, phosphorylation) in the ERBB system. The specificity of the ligand binding is shown schematically. ERBB3 does not have kinase activity. (b) Schematic phylogenic tree of the ERBB family. (c) ERBB expression profiles from various human organs. Values are taken from ProteomicsDB (ERBB1: https://www.proteomicsdb.org/proteomicsdb/#protein/proteinDetails/51261/expression, ERBB2: https://www.proteomicsdb.org/proteomicsdb/#protein/proteinDetails/51718/expression, ERBB3: https://www.proteomicsdb.org/proteomicsdb/#protein/proteinDetails/53934/expression, ERBB4: https://www.proteomicsdb.org/proteomicsdb/#protein/proteinDetails/60520/expression).