FcγRIII, synonymously also referred to CD16, is a type III Fcγ receptor which has other two identified members: a high-affinity receptor FcγRI (CD64) and a low-affinity one FcγRII (CD32). This transmembrane protein, FcγRIII, contains two extracellular immunoglobulin (Ig)-like domains with low-affinity for IgG. It is responsible for antibody-dependent cellular cytotoxicity. FcγRIII is expressed on large granular lymphocytes of both nature killer (NK)- and T-cell types. There are two different isoforms of it in humans named FcγRIIIa and FcγRIIIb, sharing 96% sequence identity in extracellular Ig binding regions. FcγRIIIa is a transmembrane receptor found on macrophages, mast and NK cells. FcγRIIIb is expressed exclusively on neutrophils and functions as the only Fc receptor anchored via a glycosyl-phosphatidylinositol (GPI) linker to the cell membrane. HER2 (Human epidermal growth factor receptor 2), also known as ERBB2, CD340 (cluster of differentiation 340), proto-oncogene Neu, is a membrane tyrosine kinase and has strongest catalytic kinase activity in HER family. Among four HER family proteins, HER2 functions as the most active signaling complex after dimerization with other members. It is encoded by the oncogene ERBB2, which is located at the human chromosome 17q12. HER2 participates in normal cell growth and found on some types of cancer cells. Its amplification is the major pathway causing HER2 receptor overexpression. HER2 is amplified in approximately 15%-20% of breast cancers and functions as the primary driver in breast tumor development and progression. The overexpressed HER2 is regarded as a valuable target in clinic therapeutics.