High-Grade Astrocytoma Variants

Abstract

Most forms of glioblastoma multiforme, despite their high grade nature, show some areas of obvious glial differentiation. Often the glial nature of the tumor is more evident at the peripheral, infiltrative edge of the tumor. This glial appearance allows for the recognition of glioblastoma multiforme as an astrocytic lesion. There are, however, a number of histologic phenotypes one might encounter in the spectrum of glioblastoma multiforme. Occasionally, the glioblastoma multiforme may be comprised mostly of small round cells with scant cytoplasm, morphologically similar to a small cell carcinoma (Fig. 5-1). Frequently, this pattern is intermixed with more recognizable astrocytic cells and is, therefore, not usually difficult to recognize. However, on a small biopsy, a differential diagnosis with metastatic small cell carcinoma may be entertained. In such cases, a combination of immunostains including glial fibrillary acidic protein (GFAP), cytokeratins, or neuroendocrine markers may resolve the issue. In most cases, at least focal GFAP positive staining will be observed in the small cell areas of glioblastoma multiforme. Keratin and neuroendocrine markers may variably stain small cell carcinomas. Certain keratin markers will also stain malignant astrocytomas. Low molecular weight keratin markers such as CAM5.2 seem to be less likely to stain astrocytomas. Often this differential depends on whether or not the patient has a known primary tumor, usually in the lung.