Dr Platzbecker on First-Line ATRA/ATO in High-Risk Acute Promyelocytic Leukemia

Uwe Platzbecker, MD, director, Medical I, University Hospital Leipzig, discusses key efficacy findings from the prospective phase 3 APOLLO study (NCT02688140) investigating the frontline combination of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) vs standard-of-care ATRA plus anthracycline-based chemotherapy in patients with high-risk acute promyelocytic leukemia (HR-APL).

Findings presented at the 2024 EHA Hybrid Congress demonstrated that the combination of ATO/ATRA plus idarubicin led to superior event-free survival (EFS) compared with ATRA/chemotherapy, Platzbecker reports. With a median follow-up of 31 months (range, 1.7-71.5 months), the 2-year EFS rates were 88% (95% CI, 80%-96%) for ATRA/ATO vs 70% (95% CI, 59%-83%) for ATRA plus chemotherapy (P = .02); 5-years EFS rates were 87% (95% CI, 79%-96%) and 55% (95% CI, 38%-78%), respectively (P = .0034).

Additionally, complete response (CR)/CR with incomplete platelet recovery rates with induction therapy were marginally higher for ATRA/ATO vs ATRA/chemotherapy, at 93% vs 90%, respectively (P = .654), Platzbecker continues. However, this difference between arms was not statistically significant. The rates of molecular resistance were also not significantly different, at 1.7% for ATRA/ATO and 5.5% for ATRA/chemotherapy (P = .268). There were no molecular remissions achieved after the final consolidation course, he notes. The 2-year cumulative incidence of relapse was 1.6% (95% CI, 0.1%-7.5%) for ATRA/ATO and 14.0% (95% CI, 6.2%-26.0%) for ATRA/chemotherapy (P = .011). Notably, 7 molecular relapses and 1 hematological relapse were reported within 2 years, which potentially contributed to the higher EFS rates with ATRA/ATO.

The 2-year overall survival (OS) rates were 93% (95% CI, 87%-99%) for ATRA/ATO and 87% (95% CI, 78%-96%) for ATRA/chemotherapy (P = .17). At 5 years, OS rates were 93% (95% CI, 87%-99%) and 82% (95% CI, 71%-95%), respectively (P = .17). Early death rates within the first 30 days were 7% vs 10%, respectively, for ATRA/ATO and ATRA/chemotherapy (P = .456). The trial also indicated lower hematologic toxicity with ATO/ATRA, showing reduced rates of thrombocytopenia and neutropenia.

Overall, these results support the potential adoption of first-line ATO/ATRA with two initial doses of idarubicin as the new SOC for high-risk APL, Platzbecker concludes. Although the study was prematurely discontinued in August 2022 due to slow recruitment during the COVID-19 pandemic and the expiration of study drug reserved for the trial, maintenance treatment and the observational period are ongoing.