Mitogen-activated protein kinase in gliosis and pilocytic astrocytoma.

Pilocytic astrocytoma (PA), featuring activation of the mitogen-activated protein kinase (MAPK) pathway, is the most common tumor of the pediatric central nervous system. However, it remains unknown whether MAPK activation is present in the reactive gliosis of non-neoplastic lesions. Therefore, we investigated the expression of MAPK in reactive gliosis associated with cavernous angiomas. Immunohistochemical expression and the extent of BRAF, ERK, p38, and JNK were investigated in 10 patients with gliosis surrounding cavernous angiomas (GS group) and 10 patients with PA (PA group). Evaluation of these parameters was scored as 0, none; 1, scarce; 2, moderate; 3, global. In the GS group, histopathologic features of PA (piloid cells, Rosenthal fibers, microcysts with eosinophilic granular bodies) were identified. Expression of ERK, and p38 was shown in all patients in the GS and PA group. Expression of BRAF was identified in 5 patients (50%) in the GS group and in 8 (80%) in the PA group. The mean score of BRAF expression in the PA group was significantly higher than that in the GS group (p = 0.019). Reactive gliosis may resemble PA in histological findings and MAPK activation. Therefore, PA could be indistinguishable from reactive gliosis with classic histopathologic and/or immunohistochemical methods.
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