IMMUNOHISTOCHEMISTRY OF SYNAPSIN-I AND SYNAPTOPHYSIN IN HUMAN NERVOUS-SYSTEM AND NEUROENDOCRINE TUMORS - APPLICATIONS IN DIAGNOSTIC NEUROONCOLOGY

Synapsin I is a phosphoprotein localized to the cytoplasmic surface of synaptic vesicles and is one of the best characterized neuron-specifi c proteins. Synaptophysin is an integral membrane glycoprotein, also l ocated on presynaptic vesicles, which has been shown to be a useful im munohistochemical marker for neuroendocrine/neuronal differentiation i n tumor diagnosis. The sensitivity and specificity of immunohistochemi cal staining for these two proteins in formalin-fixed, paraffin-embedd ed tissues was studied in a series of 67 neuroectodermal, neuroendocri ne, and non-neural tumors. Intense immunoreactivity for both synapsin I and synaptophysin was observed in tumors containing well-differentia ted neurons (gangliocytoma, ganglioglioma, neurocytoma). In these tumo rs, immunostaining was primarily concentrated along the outer surface of the cell membrane of the neuronal cells. Primitive neuroectodermal tumors (PNETs) (cerebral PNET, medulloblastoma, neuroblastoma) and mos t neuroendocrine tumors generally showed less intense and more variabl e immunoreactivity for these proteins. In most cases, immunostaining f or synapsin I was sharper and often more intense than for synaptophysi n. Some PNETs and neuroendocrine tumors that were immunoreactive for s ynapsin I did not stain for synaptophysin. We conclude that synapsin I is a reliable, sensitive immunohistochemical marker for neuronal/neur oendocrine differentiation in human neoplasms and may offer some advan tages over synaptophysin when applied to formalin-fixed, paraffin-embe dded tissues, particularly in the evaluation of primitive neuroectoder mal tumors and neuroendocrine tumors.