Ref Robbins 8/e p1159-1161;9/e p1135 Pheochromocytoma and their related counterpas in extra adrenal sites called paraganglioma, are notorious Because the only reliable indicator of metastasis potential is the presence of distant metastasis . Very malignant appearing tumors may not metastasize and benign appearing tumors may produces metastases . These tumors should all be considered " potentially malignant" .