Very Long Term Follow-up Data of Pediatric Acute Promyelocytic Leukemia Treated with Upfront Arsenic-Trioxide Based Regimens
Authors: N. Fouzia , Korula Anu , Devasia Anup Joseph , Kulkarni Uday Prakash , Samoon Yasir Jeelani , Mani Thenmozhi , Lakshmanan Jeyaseelan , Srivastava Alok , Abraham Aby , Balasubramanian Poonkuzhali , George Biju , Mathews Vikram 
Published: October 2019

Abstract
Combination of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) is currently considered the standard of care in the management of acute promyelocytic leukemia (APL). While APL is considered a highly curable malignancy there is recognition that the outcome in pediatric patients is inferior to that reported in young adults. There have been concerns raised in the past on the potential long term side effects of the use of ATO, especially in a pediatric population. There is limited long term follow up data on the use of ATO in the pediatric population. At our center we have been using ATO based regimens to treat pediatric and adult patients with APL since 1998 and hence we undertook this retrospective analysis to evaluate the long term clinical outcomes and toxicity profile in the pediatric cohort.
Data on all consecutive pediatric patients (age ≤18yrs) diagnosed with APL and treated in the Department of Haematology, Christian Medical College, Vellore, from January, 1998 to December, 2017 were included in this retrospective analysis. Of the total 73 patients with age ≤ 18yrs diagnosed during this period, 5 refused treatment and were discharged against medical advice. Treatment in the remaining 68 patients consisted of single agent ATO until 2015 (n=57), as reported previously by us (Mathews et al. Blood 2016). From 2015 combination of ATO, ATRA ± an anthracycline in induction and consolidation was administered in a risk adjusted manner (n=11). The median age was 2 years (range: 2-18) with equal gender distribution (50% each). Sixty two (91.2%) achieved complete hematologic remission (CR), 5 (7.4%) early deaths occurred from intracranial hemorrhage (n=3), neutropenic sepsis (n=1) and pulmonary thrombo-embolism (n=1), one patient did not achieve CR at the end of induction. The median time to CR was 45 days (range: 25- 62). Other acute ATO-related toxicities were low grade, transient and not associated with any mortality (transaminitis = 12 [17.6%]; ATRA like syndrome = 6 [8.8%]). With a median follow-up of 71 months, the 5 year OS and EFS of pediatric cohort (n=68) was 78.9±5.2% and 61.8±6.4% respectively (Fig 1). Among the 62 patients in CR, 21 (33.9%) relapsed at a median of 18 months (range: 5-126) from the initial diagnosis; 16 bone marrow, 3 bone marrow+CNS and 2 molecular relapses; an additional 2 patients died in remission (one viral encephalitis and another data not available). Nineteen out of 21 (90.5%) patients who relapsed received ATO based re-induction while 2 refused treatment and were discharged at request. Out of the 19 treated patients, all attained second CR. CR was consolidated with an autologous SCT (n=10) or ATO based chemotherapy (n=9). The OS and EFS of the 19 relapsed patients was 72.9±10.4% and 68±10.8% respectively.
On long term follow up of this pediatric cohort (median follow up 71 months; 18 (26.5%) > 10 years follow up and 37 (54.5%) > 5 years follow up) there were no long term renal, hepatic, metabolic complications or second malignancies noted.
Our results indicate the high efficacy and long term safety of ATO based regimens in the treatment of children with APL. Even among the relapse pediatric APL patients treated with upfront ATO, salvage chemotherapy with ATO based regimen followed by autologous stem cell transplantation is associated with excellent long term survival and is not associated with any major long term complications.

Disclosures
No relevant conflicts of interest to declare.