This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anti-Cancer, Subject name: Pharmacology
Mercaptopurine is 
Select and explain. 
A. Purine analogue, B. Nucleoside analogue, C. Pyrimidine analogue, D. Anti tumor antibiotics
A: Purine analogue
Answer: A: Purine analogue 
Explanation: Ref: Katzung, 14th ed. pg. 960; KDT, 6th ed. pg. 820* Mercaptopurine is synthetic purine used in cancer chemotherapy.* Use: Childhood acute leukemia.