The best known scoring systems for human PPGLs are the PASS Pheochromocytoma of the Adrenal gland Scaled Score (PASS), which includes 12 different histologic parameters covering morphology, invasion and proliferation [22] and the Grading system for Adrenal Pheochromocytoma and Paraganglioma (GAPP), considers histologic features together with Ki-67 proliferation index and catecholamine secretion profile [23]. This evidence concerns the gene MKI67 and hereditary pheochromocytoma-paraganglioma.