Long Term Outcome of Patients with Acute Promyelocytic Leukemia Treated with All-Trans Retinoic Acid, Arsenic Trioxide with or without Gemtuzumab Ozogamicin

Background – Combination of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) for the initial treatment of patients with low and intermediate risk acute promyelocytic leukemia (APL) has been shown to be superior to ATRA plus chemotherapy but there is limited available long-term follow up on the “chemotherapy-free” combinations.

Methods – We examined the long-term outcome of patients with newly diagnosed APL treated at our institution on three consecutive prospective clinical trials of the combination of ATRA and ATO with or without gemtuzumab ozogamicin (GO) (ID01-014; NCT01409161; NCT00413166). Initially patients received ATRA 45 mg/m² in two divided doses daily and beginning 10 days later, ATO 0.15 mg/kg daily. With subsequent studies, the schedule was modified for all patients to receive concomitant therapy with ATRA and ATO from day 1. Patients with WBC > 10 x 10⁹/L and patients whose WBC rose to greater than 10 x 10⁹/L during therapy also received a dose of GO 9 mg/m². Standard supportive care as well as steroids for prophylaxis for differentiation syndrome were administered to all patients. A bone marrow exam to assess response was performed between days 21 and 28 and, if necessary, repeated weekly. Once in CR, patients received consolidation with ATO 0.15 mg/kg daily 5 days/week for 4 weeks every 8 weeks for a total of 4 cycles and ATRA 45 mg/m² daily for 2 weeks every 4 weeks for a total of 8 months. Bone marrow assessment was performed every 3 months for 1 year and if PCR for PML-RARA was confirmed positive, a dose of GO would be administered.

Results – From July 2002 to May 2015, 183 patients have been enrolled into the three trials. During the same period a total of 235 patients with newly diagnosed APL were seen at our institution. Reasons for not being enrolled in the studies were: insurance/socio-economic in 39 (75%) and died within 48 hours of presentation in 13 (25%). Median age of the study patients was 50 years (range, 14-84). 52 (28%) were older than 60 years. Median WBC at presentation was 2.2 x 10⁹/L (range, 0.3-187.9). 52 (28%) had high risk disease with WBC > 10 x 10⁹/L and 131 (72%) had low risk disease with a WBC ≤ 10 x 10⁹/L. Cytogenetics were t(15;17) alone in 117 (64%), t(15;17) plus other in 48 (26%), other, not done, or insufficient in 18 (10%).  PCR was positive for PML-RARA in all patients (100%) with the long isoform in 104 (57%), short in 78 (43%), and both in 1 (<1%).  Overall 176 (96%) achieved CR with CR rate of 96% for low risk patients and 96% for high risk patients. Early death (occurring within 1 month of study entry) occurred in 7 (4%) and was due to 1 infection/multi-organ failure (MOF), 3 hemorrhage, 3 MOF/hemorrhage/infection. Differentiation syndrome was diagnosed in 21 (11.5%)  Other toxicities included QT prolongation in 14 (7.7%), infections in 44 (24.0%), and hemorrhagic events in 10 (5.5%).The median duration of follow-up is 39.6 months (range, 0.8 – 138.8). Six patients (3%) have relapsed including 2 (1%) with extramedullary (both CNS) relapse. The median event-free (EFS), disease-free (DFS) and overall survival (OS) have not yet been reached.  The 5-year EFS is 85%, DFS is 96%, and OS is 87% (Figures 1). The 5-year DFS and OS for low risk patients is 99% and 88%, respectively and for the high risk patients 87% and 85%, respectively (figure 2).

Conclusion – The combination of ATRA and ATO, with and without GO is effective and associated with excellent long-term DFS and OS in both low and high risk patients with newly diagnosed APL.