This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S., Subject name: Pediatrics
In a 6-year-child with ALL relapse, most common site: 
Select and explain. 
A. Bone marrow, B. Liver, C. Testes, D. Lung
A: Bone marrow
Answer: A: Bone marrow 
Explanation: a. Bone marrow(Ref: Nelson's 20/e p 2439-2441, Ghai 8/e p 599)Infants with ALL, and patients with t(4;11), have a higher risk of relapse despite intensive therapyHigher levels of MRD (>0.01%) present at end of induction suggest a poorer prognosisRelapse occurs in the bone marrow in 15-20% of patients with ALL and carries the most serious implications