 Children with ALL are usually treated according to risk groups defined by both clinical and laboratory features. This approach allows children with signs of historically very good outcome to be treated with modest therapy and to be spared more intensive and toxic treatment, while allowing children with a historically lower probability of long-term survival to receive more intensive therapy that may increase the ALL patients chance of cure. Study groups use varying criteria, with a strong emphasis on minimal residual disease MRD measurements that quantify the number of leukemic cells that remain in the patient during and after treatment. The most widely used MRD assays are based on polymerase chain reaction PCR amplification of antigen-receptor genes, and on flow cytometric detection of abnormal immunophenotypes Campana, 2010. These techniques identify the patients specific leukemia clone in bone marrow before induction treatment and measure the number of residual leukemic cells post-induction. Two widely used examples of Risk stratification protocols are the Berlin-Frankfurt-Munster BFM Protocol in Europe and the Childrens Oncology Group Protocol in USA. 