NCAM
Summary
NCAM (Neural Cell Adhesion Molecule, CD56) is an immunoglobulin-superfamily glycoprotein expressed on neurons, NK cells, and neuroendocrine tumors. It is a key IHC marker for neuroendocrine differentiation and NK-cell lineage.
Detail
NCAM mediates homophilic cell-cell adhesion important for neurodevelopment, synaptic plasticity, and axonal guidance. Heavily polysialylated (PSA-NCAM) forms reduce adhesion and promote migration during embryogenesis. Clinically, CD56 is a standard IHC marker for neuroendocrine tumors (small cell lung cancer, carcinoid, medullary thyroid, pheochromocytoma) alongside synaptophysin, chromogranin A, and NSE. It also identifies NK cells (CD56+ CD3-) and NK/T-cell lymphomas (e.g., extranodal NK/T-cell lymphoma, nasal type). Multiple myeloma plasma cells often express CD56, distinguishing them from normal plasma cells. Boards keyword: 'CD56-positive' = think NK cell or neuroendocrine.
Sources
- First Aid for USMLE Step 1 2024
- Robbins Basic Pathology 10th ed
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