NCAM / CD56, as a member of the immunoglobulin superfamily of adhesion molecules is characterized by several immunoglobulin (Ig)-like domains. The extracellular part of NCAM consists of five of these Ig domains and two fibronectin type III homology regions. NCAM is encoded by a single copy gene composed of 26 exons. However, at least 20-30 distinct isoforms can be generated by alternative splicing and by posttranslational modifications, such as sialylation. During sialylation, polysialic acid (PSA) carbohydrates are attached to the extracellular part of NCAM. Through its extracellular region, NCAM mediates homophilic interactions. In addition, NCAM can also undergo heterophilic interactions by binding extracellular matrix components, such as laminin, or other cell adhesion molecules, such as integrins. NCAM can be found in central and peripheral nerve cells, neuroendocrine tissues and at the surface of NK-cells. Also, NCAM is present in malignancies derived from these tissues and cells.