CD56 (Cluster of Differentiation 56) is a homophilic binding glycoprotein expressed on the surface of neurons, glia, skeletal muscle and natural killer cells. This antibody recognizes the basic molecule expressed on most neuroectodermally derived cell lines, tissues and neoplasms (retinoblastoma, medulloblastomas, astrocytomas, neuroblastomas, small cell carcinomas) as well as some mesodermally derived tumors (rhabdomyosarcoma).