This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Adrenal Gland, Subject name: Pathology
Which of the following is most reliable feature of malignant transformation of pheochromocytoma? 
Select and explain. 
A. Presence of mitotic figures, B. Presence of metastasis to other organs, C. Vascular/ capsular invasion, D. All of the above
B: Presence of metastasis to other organs
Answer: B: Presence of metastasis to other organs 
Explanation: - There is no histologic feature that reliably predicts malignant pheochromocytoma. - In fact, cellular & nuclear pleomorphism including presence of giant cells & mitotic figures are often seen in benign pheochromocytomas, while cellular monotony is paradoxically associated with aggressive tumors. - Even capsular and vascular invasion may be encountered in benign lesions. - Therefore, the definitive diagnosis of malignancy in pheochromocytomas is based exclusively on presence of metastases.