Cerebral astrocytic neoplasms in the adult: contribution of histologic examination to the assessment of prognosis.

Cerebral astrocytomas are the most common primary central nervous system (CNS) tumors in adults. As a group these tumors are characterized by histologic variability and inconstant prognosis. Nevertheless, microscopic examination of these tumors with identification of certain histologic features provides useful prognostic information. Evidence of anaplasia including necrosis, vascular endothelial proliferation, mitotic activity, cytologic pleomorphism, and foci of increased cellularity, when present in diffusely infiltrating astrocytic gliomas, is associated with aggressive behavior. In particular, the occurrence of tumor necrosis in anaplastic astrocytomas is reliably predictive of a highly unfavorable outcome. Specific histologic subtypes of cerebral astrocytoma with relatively benign course may also be identified. These include juvenile pilocytic astrocytoma, subependymal giant-cell astrocytoma, and, in some cases, pleomorphic xanthoastrocytoma. The critical influence of tumor location and the limitations imposed by potentially nonrepresentative biopsy material must be appreciated when assessing prognosis in cerebral astrocytomas. Prognostic data provided by histologic examination are useful in selecting treatment regimens and for evaluation of newly proposed therapies.