Improved MRD Negativity Rates in Adverse Genomic Risk B-ALL Patients with Chemotherapy / Blinatumomab Induction: Experience from the Australasian Leukaemia Lymphoma Group (ALLG) ALL06/09 Studies

Introduction: Despite the benefits conferred by pediatric treatment protocols, outcomes in adolescent and young adult (AYA) acute lymphoblastic leukemia (ALL) remain inferior to children. Poor outcomes in AYA ALL have been associated with reduced tolerability of intensive cytotoxics and higher incidence of adverse risk disease. Our earlier ALLG ALL06 study demonstrated intensive pediatric induction/consolidation could be delivered in a similar time frame as in children suggesting tolerability was not a major contributor to poor outcome in AYA ALL. ALL06 established post consolidation (TP2=d79) minimal residual disease (MRD) positivity (MRD+) and high BMI was predictive of inferior disease free- and overall survival (OS). In order to improve TP2 MRD negativity (MRD-) in B-cell disease, the ALLG ALL09 study substituted standard consolidation for blinatumomab (blin) in phase I and II of a BFM-style protocol. We present the impact of blin on outcomes in genomic cohorts from ALL09 and compare these to similar cohorts from ALL06 treated with standard chemotherapy.

Methods: Between Sep 2020 and Apr 2022, 55 patients were enrolled to ALL09. Of these, 45 had appropriate samples for genomic analyses and 39/45 had an MRD marker identified. These 39 patients formed the genomic cohort presented below. Genomic subtyping was performed using whole transcriptome sequencing, MLPA, karyotype and FISH analyses, and disease was classified into genomic adverse (AR) vs standard (SR) risk based on contemporary literature classifiers. Bone marrow MRD was assessed using ASO-PCR for IGH and TCR rearrangements, at d33 post induction (TP1), and TP2 post blin consolidation. Differences in TP2 MRD were assessed, with estimated 3 yr relapse free survival (RFS) and OS calculated using the Kaplan-Meier method.

Results: In the ALL09 cohort, median follow up was 629 days with 3 yr RFS 84.5% and OS 87.1%. In the genomic cohort, median follow up was 602 days with 3 yr RFS 88.8% and OS 93.2%, respectively. These compared favorably to 3 yr RFS and OS (both 67.5%) in the B-cell genomic cohort from ALL06.

Between ALL09 and ALL06 there were similar proportions of AR patients (73% and 62.5%, respectively). In ALL09, the most frequent subtypes were PAX5alt (18%) and PAX5 p.P80R (11%) versus KMT2Ar and DUX4r (both 17.5%) in ALL06. In ALL09, Ph-like disease represented 13% vs 12.5% in ALL06.

In the ALL09 genomic cohort, the MRD+ rate reduced between TP1 and TP2 (p<0.001), with the reduction in the rate of positivity being more pronounced in the AR cohort (AR MRD+ TP1=85% vs AR TP2=39%; p<0.001). In contrast, in ALL06 MRD+ in the AR cohort reduced by only 28% between TP1 and TP2 (p>0.05). This suggests a positive impact of blin consolidation in AR patients in ALL09. Despite improved AR MRD+ rates overall, not all genomic subtypes in ALL09 followed this trend (Table 1).

To date, there are 5 relapses in the ALL09 cohort, 4 from the genomic cohort. Of these, 1 was hypodiploid and strikingly the remaining 3 patients harbored a TCF3 rearrangement (TCF3r). All 4 relapses were significantly associated with MRD+ at TP2 (RFS: MRD-, 100% (n=14) vs MRD+, 71% (n=25); p=0.013), and all were observed in the AR genomic group. Of interest, the fifth case, outside of the genomic cohort, was classified as PAX5alt.

In ALL09, high-risk (HR) patients proceeded to intensive HR block chemotherapy with the aim of eliminating MRD prior to allogeneic transplant (SCT). In the genomics cohort 15 patients proceeded to HR therapy, n=12 were considered AR. Sustained MRD+ through HR blocks 1 and 2 was noted in patients harboring PAX5 p.P80R (3/3), KMT2Ar (2/2) and TCF3r (2/3). Of the 9 patients who proceeded to SCT, 3 had PAX5 p.P80R, 1 had PAX5alt, 2 were KMT2Ar and there was 1 each of DUX4r, hypodiploid and TCF3r. The 3 patients who remained MRD+ in the SR cohort had PAX5 p.P80R and all 3 proceeded to SCT.

Conclusion: This is the first report of the impact of blin consolidation on genomic subsets of de novo AYA ALL. Our study suggests blin sensitivity as assessed by TP2 MRD response may be genomic subtype dependent, with TCF3r associated with sustained MRD+, leading to eventual relapse (3/3 patients). In addition, the PAX5 p.P80R subset was also associated with sustained high levels of TP2 MRD+ (3/4 with an MRD marker) and SCT (3/5 patients). These results may assist with identification of AYA ALL subsets that could benefit from alternative approaches as blin becomes increasingly incorporated into front-line protocols.