A diagnostic difficulty in neuropathology practice is distinguishing reactive from neoplastic astrocyte populations. This is particularly true in small biopsy samples that lack evidence of increased cellularity or mitotic activity, microvascular proliferation, or
necrosis. We performed the current study to validate the previously reported finding that in the central nervous system, the expression of WT1 is limited to neoplastic astrocytes. We retrospectively studied
WT1 protein expression by immunohistochemistry (IHC) in 100
formalin-fixed,
paraffin-embedded brain tissue samples consisting of 3 normal control tissues, 44 cases of reactive
gliosis, 49
gliomas and 4 lesions suspicious for
glioma. In normal human cortex, WT1 staining was restricted to vascular endothelium. Most cases of reactive
gliosis (82%) showed at least focal WT1 positivity, and analysis of specimens with
electrode monitoring lesions showed an inverse relationship between WT1 expression intensity and the number of days from
electrode placement to tissue resection. All
glioma samples (100%) and all cases suspicious for
glioma (100%) showed at least focal WT1 positivity. Our results likely differ from those in the prior report because of differences in tissue fixation and IHC methodology. Thus, our findings indicate that WT1 expression alone is not a reliable feature to distinguish reactive from neoplastic astrocytes.