This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cytotoxic Anticancer Drugs, Subject name: Pharmacology
[{'content': 'Which of the following drugs is used as an immunosuppressant but lacks anticancer activity? \nSelect and explain. \nA. Methotrexate, B. 6-Mercaptopurine, C. Azathioprine, D. 5-Fluorouracil', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Azathioprine is an antimetabolite that is used as an immunosuppressant but not as an anti-neoplastic drug. It is a prodrug and is conveed to its active metabolite (6-mercaptopurine) in the lymphoid cells only.', 'role': 'assistant'}]