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Neural cell adhesion molecule 1 （NCAM-1）, also known as CD56, is a cell adhesion protein belonging to the immunoglobulin superfamily. It is expressed on various cell types including neurons, muscle cells, and immune cells like natural killer （NK） cells. NCAM-1/CD56 plays crucial roles in cell-to-cell and cell-matrix interactions during development and differentiation, regulating processes such as neurogenesis, neurite outgrowth, axonal guidance, and cell migration in the nervous system. In the immune system, it is involved in the expansion of T lymphocytes, B lymphocytes, and NK cells. NCAM-1/CD56 also triggers signaling cascades involving FYN-focal adhesion kinase （FAK）, mitogen-activated protein kinase （MAPK）, and phosphatidylinositol 3-kinase （PI3K）. Additionally, it serves as a biomarker for certain diseases, such as malignant tumors in the nervous system and neuroendocrine carcinoma.