ALL-B12

INTERVENTION: Standard Risk(SR) experimental arm: Criteria: NCI‐SR (age<10y and WBC<50,000/mm^3 ) and prednisolone good responder (PGR) and day15 BM=M1/2 and TP1 BM=M1 without HR features. Treatment: Reduced intensity BFM backbone treatment. with VCR/DEX pulse during maintenance phase. Standard Risk(SR) control arm: Criteria: NCI‐SR (age<10y and WBC<50,000/mm^3 ) and prednisolone good responder (PGR) and day15 BM=M1/2 and TP1 BM=M1 without HR features. Treatment: Reduced intensity BFM backbone treatment. without VCR/DEX pulse during maintenance phase. Intermediate Risk (IR) experimental arm: Criteria: (1) NCI‐SR (age<10y and WBC<50,000/mm^3 ) and prednisolone good responder (PGR) and day15 BM=M3 and TP1 BM=M1 without HR features. (2) NCI‐HR (age>10y or WBC>50,000/mm^3 ) and prednisolone good responder (PGR) and day15 BM=M1/2 and TP1 BM=M1 without HR features. Treatment: Standard BFM backbone treatment with intensive L‐asaparaginase during intensification phase. Intermediate Risk (IR) control arm: Criteria: (1) NCI‐SR (age<10y and WBC<50,000/mm^3 ) and prednisolone good responder (PGR) and day15 BM=M3 and TP1 BM=M1 without HR features. (2) NCI‐HR (age>10y or WBC>50,000/mm^3 ) and prednisolone good responder (PGR) and day15 BM=M1/2 and TP1 BM=M1 without HR features. Treatment: Standard BFM backbone treatment with intensive L‐asaparaginase during intensification phase. High Risk (HR) experimental arm: Criteria: at least one of following features ‐NCI‐HR (age>10y or WBC>50,000/mm^3) and prednisolone good responder (PGR) and day15 BM=M3 ‐CNS‐3 ‐prednisolone poor responder (PPR) ‐MLL‐AF4 ‐E2A‐HLF ‐Hypodiploid (<44) Treatment: BFM backbone tretment with L‐asparaginase and intrathecal therapy intensification combined with VCR intensification. High Risk (HR) control arm: Criteria: at least one of following features ‐NCI‐HR (age>10y or WBC>50,000/mm^3) and prednisolone good responder (PGR) and day15 BM=M3 ‐CNS‐3 ‐prednisolone poor responder (PPR) ‐MLL‐A CONDITION: B cell precursor Acute Lymphoblastic Leukemia PRIMARY OUTCOME: Five years event free survival of each risk group SECONDARY OUTCOME: 1) Five years event free survival, overall survival, and CNS relapse rate of whole group ; 2) Five years overall survival and CNS relapse rate of each risk group ; 3) Complete remission rate after induction (IA) and after early intensification (IB) of each risk group and whole group ; 4) Incidence of adverse events ; 5) Success rate of MRD estimation at time point 1 and time point 2. Correlation between MRD level and event free survival, overall survival ; 6) Estimation of quality of life (QOL) by Questionnaire survey to patients and families ; 7) Exploratory estimation of correlation between biological abnormality and prognosis INCLUSION CRITERIA: 1) diagnosis of B cell precursor ALL 2) age between 1 and 19 years old 3) ECOG performance status (PS) score of 0‐2 .However, PS scores up to 3 are permitted when the deterioration of PS is thought to be due to leukemia. 4) no history of previous chemotherapy or radiation therapy 5) sufficient hepatic and renal function satisfying the laboratory data listed below ; (1)T‐Bili: within 3x of age adjusted upper‐limit of normal range. (2)Creatinine: within 3x of age adjusted upper‐limit of normal range. 6) written informed consent obtained from patient or guardians.