synaptophysin
Summary
Synaptophysin is an integral membrane glycoprotein of small presynaptic vesicles in neurons and small synaptic-like vesicles in neuroendocrine cells. It is one of the most sensitive IHC markers for neuroendocrine differentiation.
Detail
Synaptophysin (p38) is a four-transmembrane glycoprotein that participates in synaptic vesicle exocytosis and recycling. By IHC, it produces a diffuse cytoplasmic granular stain in neuroendocrine cells and is highly sensitive (often more sensitive than chromogranin A) for diagnosing neuroendocrine tumors: carcinoid, small cell lung carcinoma, pancreatic neuroendocrine tumors, pheochromocytoma, medullary thyroid carcinoma, and Merkel cell carcinoma. It is paired with chromogranin A (specific) for a confirmatory panel. Unlike chromogranin (dense-core granules), synaptophysin marks small synaptic-like vesicles, so it can be positive in poorly granulated tumors. Other CNS tumors with synaptophysin positivity include neuroblastoma, medulloblastoma, and central neurocytoma.
Sources
- First Aid for USMLE Step 1 2024
- Robbins Basic Pathology 10th ed
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