High Event-Free Survival Rate with Minimum-Dose-Anthracycline Treatment in Childhood Acute Promyelocytic Leukemia: A Nationwide Prospective Study By the Japanese Pediatric Leukemia / Lymphoma Study Group (JPLSG)

Introduction: Anthracyclines (Atc) are the key drugs in the treatment of acute promyelocytic leukemia (APL) combined with all-trans retinoic acid (ATRA), however, dose-dependent risk of long-term cardiac toxicity is sometimes problematic especially in pediatric patients. To evaluate efficacy of the treatment with reduced cumulative doses of Atc in childhood APL, we conducted a nationwide non-randomized prospective study, AML-P05, in the Japanese Pediatric Leukemia/Lymphoma Study Group (JPLSG).

Patients & Methods: Between April 2006 and March 2011, forty-six children with newly diagnosed APL were enrolled in this study. All patients received at least 3-day precedence of ATRA monotherapy (45mg/m²/d for 35 days in total), followed by chemotherapeutic agents consisted of cytarabine (200mg/m²/d for 7 days) and daunorubicin (DNR, 45mg/m²/d for 3 days) as the first induction therapy. The second induction therapy and subsequent 3 courses of consolidation therapy consisted of ATRA, either high- or intermediate-dose of cytarabine, triple intrathecal injection, and single dose of Atc; 10mg/m² of mitoxantrone (MIT) in the first 2 courses and 45mg/m² of pirarubicin (THP) in the last 2 courses. Finally, patients received one-year maintenance therapy with ATRA for 15 days every 3 months.

Results: Among the 46 patients registered in this study, 3 were excluded because of PML/RARA negativity, and the remaining 43 patients including 2 with molecular variants were evaluated. The median age at diagnosis was 9 years (range, 11 months to 15 years old). The median follow up period was 4.47 years (0.00-7.45 years). FLT3-ITD was positive in 6 out of 40 patients examined. Two patients died during induction therapies; one of coagulopathy in first course and the other of infection in second course. Two patients developed differentiation syndrome but resolved with temporary cessation of ATRA and supportive therapies. Three patients did not achieve complete remission (CR) after 2 courses of induction therapy, and overall CR rate was 85.7% (36/42, 95%CI: 71.5-94.6%). Neither cardiac adverse events nor treatment-related death were observed during consolidation and maintenance therapies. Three patients exhibited relapse during or after maintenance therapy, and another one developed secondary acute myeloid leukemia. Consequently, the 3-year event-free (EFS) and overall survival rate were 83.6% (95%CI: 68.6-91.8%) and 90.7% (95%CI: 77.1-96.4%), respectively. Age less than 4 years old at diagnosis and non-M1 marrow after first induction therapy were associated with lower EFS. High WBC count (>10,000/μL), low platelet count (<40,000/μL), FLT3-ITD positivity, and additional chromosomal abnormality did not influence the risk of events.

Conclusions: According to the JPLSG criteria of Atc equivalents, cumulative Atc dose in this study was converted to 246mg/m2 of doxorubicin (for 1:0.83 for DNR, 1:4 for MIT, and 1:0.6 for THP). The dose was much lower than that in recent US or European protocols, especially in those designed primarily for adult APL patients where more than 600mg/m² of Atc were used. Comparing with these studies, we have achieved equivalent good results with minimum does of Atc. Therefore, single administration of Atc in each consolidation phases seems sufficient in the treatment of childhood APL.

This trial is registered with UMIN Clinical Trials Registry (UMIN-CTR, URL: http://www.umin.ac.jp/ctr/index.htm), number UMIN000000645