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.