Immunohistochemical expression of tyrosine kinase (Trk) receptor proteins in mature neuronal cell tumors of the central nervous system.

The interactions of neurotrophins with the Trk family of tyrosine kinase receptors result in growth and maturational changes in neuronal cells. Although the histogenesis of brain tumors composed of mature neuronal cells is still not completely understood, neurotrophins and Trk receptors may be involved in the evolution, maturation, and persistence of these tumors. The clinical and anatomic pathological features of 8 primary neuronal cell tumors (ganglioglioma: 3 cases, cerebral neurocytoma: 3 cases, intraventricular neurocytoma: 2 cases) occurring in the central nervous system (CNS) have been examined. In addition to routine histological examinations, immunohistochemistry was used to evaluate the expression of neurotrophin receptors (TrkA, TrkB) and of neuronal differentiation markers such as neuron-specific enolase, neurofilament, synaptophysin, and chromogranin A. While neither TrkA nor TrkB expression was demonstrated in 2 intraventricular neurocytomas, the remaining 6 tumors did show positive immunohistochemical staining for TrkA and/or TrkB proteins; for TrkA protein, ganglionic cells showed membraneous or cytoplasmic staining, while small non-ganglionic neuronal cells with scant cytoplasm occasionally showed positive cytoplasmic immunoreactivity. For TrkB protein, small non-ganglionic neuronal cells showed a more intense immunoreaction than ganglionic cells. Gangliogliomas with high TrkA and TrkB expression showed higher levels of neuronal differentiation, as demonstrated by the neuron-specific enolase and neurofilament immunoreactivity. The existence of neurotrophin receptors in the tumor cells thus suggests that neurotrophic influence are involved in the evolution and subsequent cellular maturation in neuronal cell tumors of the CNS.