Response Adapted Therapy in ETV6/RUNX1-Positive Childhood Acute Lymphoblastic Leukemia Treated per Modified St Jude Total XV Study

Introduction: ETV6-RUNX1 is the most common genetic aberration in childhood acute lymphoblastic leukemia (ALL), occurring in approximately 25% of cases with a precursor-B phenotype. The presence of ETV6-RUNX1 has been associated with a relatively low rate of relapse in multiple studies. Relapses tend to occur late and have a better salvage rate than other ALL subtypes. Moreover, conflicting data in literature regarding the prognostic significance of ETV6-RUNX1 after accounting for age, initial count and treatment intensity. We sought to study the clinical features, therapy response in newly diagnosed ETV6-RUNX1-positive treated at King Hussein Cancer Center.

Methods: Patients were treated per modified St Jude Total (XV) study, risk stratification was further refined by including minimal residual disease (MRD)measurements on day 15 and day 46 of remission induction therapy. Patients with the ETV6- RUNX1 fusion or hyperdiploidy without CNS or testicular disease and a satisfactory early MRD decline (<1% on day 15 and <0.01% on day 46) were classified as being low-risk for relapse and were treated on lower -risk arm regardless of age and leukocyte count.

Results: Seventy patients (n=70) with ETV6-RUNX1-positive treated at our institution between May 2006 to October 2017. The median age at diagnosis, 5.8 years (range, 1.5-10.8). ETV6-RUNX1 was associated with favorable age between 1- and 6-years in 55 patients (79%), male gender in 41 patients (59%), initial leukocyte count <10 in 39 patients (56%), CNS status 1 in 100% of patients. The majority, n= 58 (83%) of patients had NCI standard risk (SR) and n=12 (17%) had NCI high risk (HR). Sixty-six patients (94%) had MRD <1% at day 15 and all patients achieved remission with MRD<0.01% at day 46 of remission induction. All patients were treated as LR ALL per modified St Jude total XV protocol. At median follow up of (36 months; range, 26 to 154), in the subgroups of ETV6-RUNX1-positive patients classified as NCI standard risk (SR)and NCI high risk (HR) the 5-year EFS estimates were 94.1% ± 3.2 and 82%±1(P=.13), 5-year OS estimates were 100% and 92% ± 8 (p=0.31) respectively.

Conclusion: MRD treatment schema in ETV6/RUNX1 -positive patients have excellent outcomes if they achieved favorable response at day 15 and end of remission induction regardless of the age and Initial leukocyte count. Treatment reduction is feasible and declared safe for children with NCI-HR who are predicted to have a low risk of relapse on the basis of rapid clearance of MRD post remission induction therapy.