Improved Outcome with ATRA-Arsenic Trioxide Compared to ATRA-Chemotherapy in Non-High Risk Acute Promyelocytic Leukemia – Updated Results of the Italian-German APL0406 Trial on the Extended Final Series

Background: We recently showed that the combination of ATRA and arsenic trioxide (ATO) is at least not inferior and possibly superior to standard ATRA and chemotherapy (CHT) in the front-line management of low/intermediate risk APL (Italian-German APL 0406 trial; Lo-Coco et al., NEJM 2013). We report herein on the extended and final series of 276 patients (162 were in the previous report) with the last case being enrolled into the study in January 2013.

Methods: The APL0406 study was a prospective, open-label, randomized intergroup trial conducted by the Italian GIMEMA and the German SAL and AMLSG study groups. Eligible patients were adults aged 18-<71 years with newly diagnosed, genetically confirmed, non-high-risk (WBC≤10x10⁹/L) APL. Patients were randomized to receive the ATO+ATRA combination originally developed by the MD Anderson Cancer Center group, or the Italian AIDA2000 protocol (Estey et al., Blood 2006 and Lo-Coco et al., Blood 2010). Patients in the ATRA-ATO arm received ATO 0.15/kg plus ATRA 45 mg/m² daily until CR, then ATO 5 days/week, 4 weeks on 4 weeks off, for a total of 4 courses and ATRA 2 weeks on and 2 weeks off for a total of 7 courses. Patients in the ATRA-CHT arm received the standard AIDA (ATRA+Idarubicin) induction followed by 3 cycles of anthracycline-based consolidation together with ATRA and low dose CHT and ATRA for maintenance. The primary study objective was EFS at 2 years.

Results: A total of 254 patients were evaluable for response to induction. CR was achieved in 122/122 (100%) in the ATRA-ATO versus 128/132 (97%) in the ATRA-CHT arm (P=0.12). Four patients died during induction in the ATRA-CHT arm. After a median follow-up of 36 months (range 1-75 months), the 2-year EFS was 98% and 84.9% in the ATRA-ATO and ATRA-CHT groups respectively (P= 0.0002), The 2-year cumulative incidence of relapse (CIR) rate was 1.1% and 9.4%, respectively (P=0.005) and, finally, the 2-year overall survival (OS) rate was 99.1% vs. 94.4% (P=0.01) for ATRA-ATO vs ATRA-CHT, respectively.

Conclusions: The data on this extended cohort demonstrate a significantly augmented survival benefit coupled to a higher antileukemic efficacy provided by ATRA-ATO as compared to ATRA-CHT, in low/intermediate risk APL. These results further support ATRA-ATO as the new standard of care in this clinical setting.

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