This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
Which of the following criteria can be used to determine if a pheochromocytoma lesion is benign or malignant 
Select and explain. 
A. Blood vessel invasion, B. Cannot be determined by microscopic examination, C. Hemorrhagic and necrosis, D. Nuclear pleomorphism
B: Cannot be determined by microscopic examination
Answer: B: Cannot be determined by microscopic examination 
Explanation: 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" .