Minimal residual disease comparison between Ig/TCR PCR versus NGS assays in children with Philadelphia chromosome-positive acute lymphoblastic leukemia: A report from the COG AALL1631 study.

10023 Background: Minimal residual disease (MRD) assessment by immunoglobulin/T-cell receptor (Ig/TCR) polymerase chain reaction (PCR) is currently being used in the international pediatric Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph + ALL) trial EsPhALL2017/AALL1631 for risk stratification. MRD concordance has previously been demonstrated between Ig/TCR PCR and flow cytometry in Ph + ALL. We sought to assess concordance of MRD assessment between conventional Ig/TCR PCR and next-generation sequencing (NGS) assays. Methods: MRD was assessed in all pts on AALL1631 by Ig/TCR PCR at end-induction IB; those with MRD <5x10 -4 were classified as standard-risk (SR) and randomized to treatment with imatinib and one of two chemotherapy regimens without hematopoietic stem cell transplant (HSCT), whereas pts with end-induction 1B MRD ≥ 5x10 -4 were considered high-risk (HR) and assigned to HSCT after consolidation chemotherapy. Residual diagnostic and end-induction IB samples from consenting pts were assessed for NGS MRD by the clonoSEQ assay (Adaptive Biotechnologies) in blinded fashion and subsequently compared to Ig/TCR MRD to determine concordance as related to MRD-based HSCT recommendations ( ie, MRD ≥ 5x10 -4 consistent with HR group assignment). MRD values were calculated using the kappa statistic for agreement above chance. Results: Sixty-seven pts had matched samples available for MRD assessment at end-induction 1B by both Ig/TCR PCR and NGS (Table). NGS MRD was evaluable for all 67 pts and stratified as 62 SR (<5x10 -4 ) and 5 HR (≥5x10 -4 ). In contrast, Ig/TCR PCR results were inevaluable for 3 pts (unsatisfactory sample quality) and indeterminate (positive, but not quantifiable) in 4 pts. Of the remaining 60 pts, 55 met SR and 5 HR criteria using Ig/TCR PCR. There was only 1 discordant case between the two methods for MRD-based HSCT recommendation among these 60 pts with a kappa statistic for agreement above chance of 0.88. Conclusions: NGS and Ig/TCR PCR assays were highly concordant in MRD assessment for risk stratification at a threshold of 5x10 -4 in pediatric pts with Ph + ALL enrolled on AALL1631. Of note, the NGS assay yielded MRD results amenable for risk stratification in 100% pts compared to 89.6% for the Ig/TCR PCR methodology. These data support the use of NGS MRD testing for risk stratification in pediatric Ph + ALL.[Table: see text]