<prompt> Commonest site of extramedullary relapse of ALLCNSLungLiverTestis  <response>: 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 marrow20,central nervous system5,and testis3.Relapse in extramedullary sites,paicularly testes,is more ourable in terms of survival. Reference:Essential pediatrics-Ghai,8th edition,page no:604 