Immunohistochemical demonstration of alpha-1-proteinase inhibitor in brain tumors.

Using light microscopy and immunoperoxidase methods (PAP), the presence of alpha-1-proteinase inhibitor (API) was studied in seventeen brain tumors and four normal brain samples. The brain tumors included four glioblastomas, five low-grade gliomas, two metastatic lung carcinomas, two acoustic schwannomas, and four meningiomas. Normal brain displayed a finely granular intracytoplasmic staining confined to neuronal cells. Glial cells were negative for API. Fifteen of the 17 brain tumors were positive for API. Only two of five low-grade gliomas were negative for API. Glioblastoma and metastatic tumors exhibited the strongest positivity followed by acoustic neuroma, meningioma, and low-grade glioma. All positive samples exhibited finely granular intracytoplasmic API, and 50% exhibited extracellular API positivity. Metastatic and glioblastoma tumors demonstrated prominent extracellular API staining. Our results support the concept of a local production of API by brain tumors.