ErbB3， also called Her3 （human epidermal growth factor receptor 3）， is a type I membrane glycoprotein that is a member of the ErbB family of tyrosine kinase receptors. ErbB family members serve as receptors for the epidermal growth factor （EGF） family of growth factors. Among ErbB family members， ErbB3 is unique in that it contains a defective kinase domain. ErbB3 is expressed in keratinocytes， melanocytes， skeletal muscle cells， embryonic myoblasts and Schwann cells. Monomeric ErbB3 serves as a low affinity receptor for the heregulins （HRG）. ErbB3 can induce specific antibody production in vivo， hence to inhibit tumor cell growth. ErbB-3 can be used to treat early， medium and advanced or post-operative breast cancer with over-expression of ErbB2. According to its mechanism of action， ErbB3 is classified as a therapeutic for cancer.
