Excellent Outcome in Pediatric AML with Response Guided Chemotherapy without Allogeneic HSCT in First Complete Remission: Results from Protocol DB-AML01

Background: Contemporary treatment schedules for pediatric acute myeloid leukemia (AML) have improved 5 year-overall survival rates up to 70% . These schedules usually consist of 4 to 5 intensive courses mainly based on cytarabine (AraC) and anthracyclines, with allo-HSCT upfront in a subset of patients . Long-term side effects such as late cardiotoxicity caused by high cumulative anthracycline dosages are a major concern. Therefore, the DCOG/BSPHO collaboration adapted the NOPHO 2004 protocol to DB-AML01 to reduce cumulative anthracyclines from 420-450 mg/m² to 300-330 mg/m² and to omit HSCT in CR1.

Material: The treatment consisted of 5 chemotherapy courses: first induction course AIET (AraC conventional dose and Idarubicin (Ida) 36 mg/m2); second induction course AM (AraC conventional dose and Mitoxantrone (Mitox) 30 mg/m2) when blasts at day 15 < 5% or FLA-DNX (high dose AraC and Daunoxome (DNX) 180 mg/m2) when blasts > 5% at day 15 or t(8;21) AML; 3 consolidation courses (high dose AraC with Etoposide as course 3 and 5 and in between high dose AraC alone). Cumulative dose of AraC is 43,4 gr/m2 and of anthracyclines 300 mg/m² for patients receiving AIET+AM or 330 mg/m² for patients receiving AIET/FLA-DNX.

Results: From 2010 to 2014 a total of 113 children with AML, median age 6.0 yrs (range 0-16), gender 56 males, were included. Second induction course was AM in n=75 and FLA-DNX in n= 33. Death in induction occurred in 4 patients, CR rate was 102/113 (90.3%) and 7 patients were refractory after induction. The later events were death in CR (n=2), relapse in CR (n=40), and secondary malignancies (n=0). HSCT was given to 3 patients in CR1 (physician's decision). Median follow up time is 2.6 years (range (range 1-5). Probability of EFS at 2 years was 60% (95% CI 49-69%) and 2-yr OS was 76 (95% CI 66-83%)77.9%. Especially inv 16 (n=10) and t(8;21) AML (n=16) had an excellent outcome (inv 16:2-yr EFS: 70% (95% CI 32-89%) and 2-yr OS 91% (95% CI 51-99%) resp t(8;21):2-yr EFS: 87% (95% CI 57-97%) and OS: 94% (95% CI 63-99%)), EFS nor OS in other genetic subgroups such as FLT3-ITD and MLL rearrangements were significantly different from the total group. Children with an older age (> 10 years) (n=34) or high WBC count (>50.10⁹/l) (n=41) had the poorest 2-yr EFS: 51 (95% CI 33-67%) resp EFS: 40% (95% CI 24-56%), whereas OS was not significantly worse. For the patients with a relapse, 32 achieved a second CR and 4 a partial remission (90%) . In second CR 34 patients received an allo-HSCT. Until now 26 of the 40 patients are still in second CR.

Conclusion: The DB-AML01 outcome data suggest that the choice of high cumulative doses of AraC with moderate cumulative doses of anthracyclines up to 300-330 mgr/m² results in a favorable overall survival for particularly those children with t(8;21), inv (16) AML, young age or lower WBC counts. Children with relapsed AML could be rescued with second line treatment and allo-HSCT. These results underscore the relevance of identification of subgroups of pediatric AML patients, based on age, WBC count and t(8;21) or inv 16, curable with "lower risk" treatment arms without allo-HSCT in CR1.