Phase II trial shows high remission and survival with frontline ATRA-ATO for newly diagnosed APL

All-trans retinoic acid (ATRA) combined with arsenic trioxide (ATO) has become the international standard of care for newly diagnosed acute promyelocytic leukemia (APL), demonstrating superior efficacy and safety over ATRA-chemotherapy regimens. However, in Japan, ATO has been approved only for relapsed/refractory APL, and prospective data on its frontline use are lacking. We conducted FBMTG-APL2017, a prospective multicenter phase II trial in Japan, to evaluate ATRA-ATO in newly diagnosed APL patients, including both low-intermediate-risk and high-risk groups. Eighty-one patients were enrolled between 2017 and 2021 and treated with ATRA plus delayed ATO during induction, followed by four cycles of ATRA-ATO consolidation. Complete remission was achieved in 95.1% of patients. With a median follow-up of 55 months, 3-year disease-free survival (DFS) and overall survival (OS) were 93.6% and 95.0%, respectively, consistent with international ATRA-ATO trials. DFS was 96.9% in low-intermediate-risk and 80.0% in high-risk patients, with no significant difference. Molecular remission was achieved in 99% after consolidation, and only two molecular relapses occurred. Differentiation syndrome developed in 56.8% but was generally manageable, with only one fatal case; early death occurred in 4.9%, comparable to international data. These results provide the first prospective evidence in Japan that frontline chemo-free ATRA-ATO is highly effective and safe across all risk groups. They support its adoption as a new standard therapy and bridge the gap with established global practice. Trial Registration: Japan Registry of Clinical Trials: jRCTs071180040.