We used a modified CALGB 19802 [
15,
16] treatment protocol that comprised 6 courses of chemotherapy administered in the order of A-B-C-A-B-C regimens, followed by a maintenance phase. Induction chemotherapy (course A) was a 21-day course consisting of cyclophosphamide (CPM; 1200 mg/m
2 on day 1), daunorubicin (DNR; 60 mg/m
2 on days 1, 2, and 3), vincristine (VCR;1.3 mg/m
2 [maximum 2 mg] on days 1, 8, 15, and 22), L-asparaginase (3000 U/m
2 on days 9, 11, 13, 16, 18, and 20), and prednisolone (PSL; 60 mg/m
2 [max 100 mg]). Granulocyte-colony stimulating factor (nartograstim) was administered starting from day 4 and continued until neutrophil recovery. For patients aged 55 years or older, the doses of CPM and DNR were reduced to 500 mg/m
2 and 50 mg/m
2, respectively. Furthermore, PSL therapy was shortened to 7 days in these patients. The first consolidation therapy (course B) consisted of mitoxantrone (MIT; 10 mg/m
2 on days 2 and 3), cytarabine (AraC; 2000 mg/m
2/day on days 1, 2, 3, and 4) and intrathecal administration of methotrexate (MTX; 15 mg/body on day 1). For patients aged 55 years or older, the doses of MIT and AraC were reduced to 7 mg/m
2 and 1500 mg/m
2/day, respectively. The second consolidation therapy (course C) consisted of VCR (1.3 mg/m
2 [max 2 mg] on days 1, 8, and 15) and MTX (1500 mg/m
2 on days 1, 8, and 15) with leucovorin rescue and intrathecal MTX on days 1, 8, and 15. The patients received the following maintenance chemotherapy on a monthly basis: PSL, 60 mg/m
2 on days 1–5; VCR, 1.3 mg/m
2 (max 2 mg) on day 1; oral MTX, 20 mg/m
2 weekly; and oral 6-mercaptopurine, 60 mg/m
2 daily. MRD status was evaluated after the induction therapy (first course A) and after the second consolidation therapy (first course C). Patients with positive MRD following the second consolidation therapy were considered to be indicated for allogeneic HSCT as soon as possible. Eligible donors included HLA-identical related, HLA-identical unrelated donors from Japan Marrow Donation Program, and cord blood from Japan Cord Blood Bank Network. Conditioning before allogeneic HSCT and prophylaxis for graft-versus-host disease was performed according to each institutional standard.