Neural cell adhesion molecule 1 (NCAM1,also known as CD56) is a cell adhesion glycoprotein of the immunoglobulin (Ig) superfamily. It is a multifunction protein involved in synaptic plasticity,neurodevelopment,and neurogenesis. NCAM1 is expressed on human neurones,glial cells,skeletal muscle cells,NK cells and a subset of T cells,and the expression is observed in a wide variety human tumors,including myeloma,myeloid leukemia,neuroendocrine tumors,Wilms' tumor,neuroblastoma,and NK/T cell lymphomas. Three major isoforms of NCAM1,with molecular masses of 120,140,and 180 kDa,are generated by alternative splicing of mRNA . The glycosylphosphatidylinositol (GPI)-anchored NCAM120 and the transmembrane NCAM140 and NCAM180 consist of five Ig-like domains and two fibronection-type III repeats (FNIII). All three forms can be posttranslationally modified by addition of polysialic acid (PSA) . Several other isofroms have also been described .