Recently, there have been studies conducted with mesothelioma, various epithelial tumors, meningioma, and pleomorphic xanthoastrocytoma (PXA) in order to use methylthioadenosine phosphorylase (MTAP) immunohistochemical expression loss as a surrogate biomarker to detect CDKN2A HD status (14–21). The gene discussed is MTAP; the disease is meningioma.