Patterns of MiB-1 staining of brain tumors: microwave-antigen retrieval as a tool in diagnostic pathology

MiB-1 antibody staining can be carried out on formalin fixed, paraffin embedded tissue only if microwave antigen retrieval is performed. This method was used to identify proliferating cells in archival paraffin sections of 137 cases of human brain tumors. The tumors concerned were astrocytomas (57), glioblastomas (16), oligodendrogliomas (11), mixed gliomas (8), ependymomas (9), subependymoma (2), medulloblastomas (4) and meningiomas (30). For the tumors which were histologically graded (the astrocytomas, oligodendrogliomas and ependymomas), generally the scores of MiB-1 staining were correlated with the tumor grade, although there were exceptions to this rule, for example, a few low grade tumors displayed high MiB-1 counts while some highly malignant brain tumors failed to display any positive staining for MiB-1, despite having high mitotic counts. This phenomenon was probably due to loss of proliferating antigens. In the MiB-1 positive sections, hot spots with a high mitotic activity could be identified with ease and the abnormal morphology of the tumor nuclei and of the atypical mitoses were highlighted by the contrasting intensily brown staining. In addition, the dividing cell type could be easily identified and differences in mitotic behavior of invasive and necrotic parts of tumors could be observed.