Carbonic Anhydrase IX (CA9) Overexpression and Negative PAX8 Staining Can Be Used to Confirm Hemangioblastomas

Introduction/Objective: Hemangioblastomas are indolent brain tumors consisting histologically of atypical stromal cells and a large number of blood vessels lined by endothelial cells. The tumors are often associated with either von Hippel- Lindau (VHL) syndrome or sporadic mutation of VHL genes. As CA9 is a marker of the hypoxic inducible factor-alpha1 cascade, its overexpression has been well known to present in clear cell renal cell carcinoma that involves the mutation of VHL gene. A few studies demonstrate overexpression of CA9 in hemangioblastomas, but not in other primary brain tumors such as gliomas and meningioma. Our two cases were used to determine if positive CA9 and negative PAX8 immuno-stains were useful markers to support the diagnosis of hemangioblastomas. Methods/Case Report: One patient was a 50-year-old man and the other patient was a 75-year-old man. Two lesions were identified in the cerebellum with typical appearance of vascular channels intermingled with atypical stromal cells showing clear cell cytoplasm. The endothelial cells were positive for CD34 and ERG. The stromal cells were weakly positive for inhibin but negative for the endothelial markers GFAP, pancytokeratin and PAX8, ruling out primary glioma and metastatic clear cell renal carcinoma. The atypical stromal cells with clear cytoplasm in both tumors, however, showed strong and diffuse membranous staining for CA9 (3+). The overall findings supported the morphologic diagnosis of hemangioblastomas in both patients. Results (if a Case Study enter NA): NA Conclusion: Our preliminary data indicates that positive CA9 and negative PAX8 stains are a useful pair of markers to support a diagnosis of hemangioblastoma and differentiate them from metastatic clear cell renal cell carcinoma. Additionally, CA9 can help confirm the diagnosis of hemangioblastoma when inhibin is weak or nearly negative.