Single Agent Arsenic Trioxide Regimen for the Treatment of Newly Diagnosed Acute Promyelocytic Leukemia: Initial Results of a Multicenter Randomized Controlled Study From India to Study the Optimal Duration of Arsenic Trioxide Maintenance Therapy (IAPLSG04).

Abstract 2082

Poster Board II-59

Single agent arsenic trioxide (ATO) has proven efficacy in the management of newly diagnosed cases of acute promyelocytic leukemia (APL). To validate findings of an initial single center experience (Blood 2006:107; 2627) with this low cost, well tolerated, effective regimen, a multicenter study was undertaken in a resource constrained environment. Additionally, in an effort to improve on the earlier experience and study the role of duration of maintenance on reducing late relapses, patients were randomized to 6 vs. 12 months of ATO maintenance (ClinicalTrials.gov Identifier:NCT00517712).

From July, 2004 to December, 2008, 182 patients were initially screened and enrolled based on morphological diagnosis of APL from 7 centers in India. Diagnosis was subsequently confirmed by molecular methods. Twenty seven cases were excluded from analysis (6 RT-PCR negative, 4 IC bleed at diagnosis, 5 septic/pneumonia at diagnosis, 9 withdrew consent prior to randomization and some were treated with other protocols, 1 withdrawn by investigator prior to randomization). Patients were treated with single agent ATO at standard doses (10mg/day for adults and 0.15mg/kg/day for pediatric patients) for up to 60 days in induction; this was followed by a 28 day consolidation after a 4 week break. Four weeks after completion of consolidation patients who were in molecular remission were randomized to 6 vs. 12 months of maintenance therapy with ATO administered for 10 days/month. Hydroxyurea was permitted for control of leucocytosis. Anthracyclines were permitted in induction for patients presenting with or WBC count rising >20×10⁹/L in the first week, >50×10⁹/L in the second week and for those who developed a differentiation syndrome. Of the 155 patients who could be evaluated 136 (87.7%) achieved hematological remission (CHR). One patient had primary induction failure and was removed from the study while the other 18 were induction deaths at a median of 17 days (range: 4 – 69). During induction, 52 (33.5%) patients received an anthracycline and 116 (75%) received hydroxyurea. A differentiation syndrome was documented in 25 (16%) cases and was fatal in one. Grade III/IV non hematological toxicity was seen in 26 (16.7%), which resolved in the majority after discontinuing ATO for a short period. One hundred and thirty six patients were randomized, 64 (47%) and 72 (53%) into a 6 and 12 month maintenance regimen respectively. A protocol change after randomization was done in 3 cases for persistent toxicity. Five (3.6%) patients did not complete the scheduled maintenance regimen due to poor compliance or was discontinued by the investigator. At a median follow up of 24 months, the 3-year Kaplan-Meir estimate of overall survival (OS), event free survival (EFS) and disease free survival (DFS) of the entire cohort was 76.87±4.33%, 71.57±4.64% and 80.69±4.77% respectively. Fourteen patients relapsed, the median time to relapse was 19.3 months (range: 9-51). The baseline characteristics of the two groups (6vs12 months) were not significantly different. Post randomization, the two groups were analyzed on an intention to treat basis. The OS, EFS and DFS of the two groups were not statistically significantly different. There was also no evidence that the group that received 12 months of maintenance had any increased incidence of toxicity.

Single agent ATO based regimen as reported previously is well tolerated and results in durable remissions. Longer follow up is required to see if 12 months of maintenance therapy reduces risk of late relapses.