Diffuse bone marrow metastasis by glioblastoma: premortem diagnosis by peroxidase-antiperoxidase staining for glial fibrillary acidic protein.

Extraneural metastases from malignant glioma and glioblastoma are believed to be rare. The most common sites of metastases are lung, lymph nodes, bone, and liver. We recently encountered two patients with glioblastoma multiforme who presented with pain and thrombocytopenia caused by diffuse metastasis to bone marrow. A premortem diagnosis was established in the first patient with the aid of peroxidase-antiperoxidase staining of the bone marrow biopsy specimen for glial fibrillary acidic protein, a glial-specific marker. In the second patient glial fibrillary acidic protein staining confirmed the glial nature of the primary brain tumor as well as the metastatic tumor in bone marrow. The first patient also had metastatic nodules on the pleural surface and on the fifth rib. All three metastatic foci had similar cellular morphology, suggesting selection of a population of tumor cells with extraneural metastatic potential.