MITOSIS IDENTIFICATION IN DIFFUSE GLIOMAS - IMPLICATIONS FOR TUMOR GRADING

BACKGROUND. The histologic differentiation of mitotic figures is a cor nerstone of several highly predictive grading systems for gliomas. In some systems, the presence of even a single mitotic figure is sufficie nt to classify an astrocytoma as high grade. However, the extent of mi croscopic examination necessary to exclude the presence of significant mitotic activity has not been determined. METHODS. Hematoxylin and eo sin-stained slides from 410 astrocytomas and 107 oligodendrogliomas/ol igoastrocytomas were reviewed until the first mitosis was identified o r 100 400x fields had been reviewed without identification of a mitosi s. The number of the field in which the first mitosis was found was co rrelated with diagnosis, grade, and survival. RESULTS. A review of 50 400x fields was necessary to achieve a >90% sensitivity in identifying a mitosis in a Grade 3 astrocytoma specimen, compared with 20 400x fi elds in anaplastic (Grade 3 and 4) oligodendroglioma specimens. For Gr ade 3 astrocytomas, there was a significant independent correlation be tween survival and the field in which the first mitosis was found (P = 0.02). For the oligodendroglial tumors, there was a strong correlatio n between the number of fields counted until the first mitosis was fou nd and grade (P < 0.0001). CONCLUSIONS. The evaluation of mitotic acti vity offers more prognostic information than can be obtained by the si mple approach of noting only their presence or absence. Data were acqu ired regarding the diligence of the microscopic examination necessary to evaluate the presence or absence of mitotic activity. A 1 cm x 0.1 cm needle biopsy contains adequate tissue to evaluate mitotic activity for the purpose of histologic grading; however, this adequacy is depe ndent on the sample's being representative and composed entirely of ce llular tumor. (C) 1998 American Cancer Society.