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Representative sampling of gliomas at biopsy is essential for correct assignation of histological grade and subsequent patient management. If sampling is unrepresentative, tissue devoid of mitoses or necrosis may be obtained and result in a falsely low glioma grade. The objective of the present study was to assess whether the MIB-1 labelling index of glioma tissue cores specifically constructed so as to replicate ‘unrepresentative’ astrocytoma biopsies would predict the real or actual glioma grade. Tissue microarrays were prepared from 134 samples of low-grade astrocytoma (LGA; WHO grade II), anaplastic astrocytoma (AA) and glioblastoma multiforme (GBM). Donor blocks were sampled in such a way as to avoid mitoses, necrosis and endothelial hyperplasia. Immunohistochemistry was performed using the Ki-67 (MIB-1) proliferation marker, and the percentage of MIB-1-positive cells per core was calculated. Mean MIB-1% values for LGA (n = 47), AA (n = 38) and GBM (n = 46) were mean (SD) 0.54 (0.82), 5.68 (6.69) and 7.21 (7.98); ranges 0–3.07, 0–30.08 and 0–29.08, respectively. An MIB-1% count of >3.07 excludes LGA, but an MIB-1% count of <3.07 does not exclude GBM or AA. It is concluded that in unrepresentative glioma biopsy material, MIB-1 labelling may be used to exclude LGA, but cannot be used to distinguish between GBM and AA.
Astrocytomas in adults demonstrate considerable cellular heterogeneity, and pathological grading is the most significant predictor of clinical outcome.1 While grading may be suggested radiologically, it is recommended that all astrocytomas be biopsied to establish a correct diagnosis and grade. The presence of mitoses and necrosis is a key adjunct in the grading of astrocytomas. Mitoses are a feature of high-grade gliomas, including anaplastic astrocytomas (AAs), and would not generally be seen on a biopsy of a low-grade astrocytoma (LGA). Moreover, the presence of palisaded necrosis in an astrocytoma distinguishes GBM from AA.
Inadequate or unrepresentative tissue …
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