This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Childhood tumors, Subject name: Pediatrics
Commonest site of extramedullary relapse of ALL 
Select and explain. 
A. CNS, B. Lung, C. Liver, D. Testis
A: CNS
Answer: A: CNS 
Explanation: Despite success of modern treatment,20-30% of children with ALL relapse.The main cause of treatment failure in leukemia is relapse of the disease.Common sites of relapse are the bone marrow(20%),central nervous system(5%),and testis(3%).Relapse in extramedullary sites,paicularly testes,is more ourable in terms of survival. Reference:Essential pediatrics-Ghai,8th edition,page no:604