Integrated Use of Minimal Residual Disease Classification and IKZF1 Alteration Status Accurately Predicts 79% of Relapses In Pediatric Acute Lymphoblastic Leukemia

Abstract 272

The response to therapy as determined by minimal residual disease (MRD) is currently used for stratification in treatment protocols for pediatric acute lymphoblastic leukemia (ALL). Even though MRD classification clearly identifies patients at low or at high risk for relapse, it also results in a large intermediate group (50 to 60% of patients), which still contains approximately half of all relapse cases. To improve risk stratification, we evaluated the added value of the IKZF1 alteration status, recently identified as a prognostic factor, in precursor-B-ALL patients. In an unbiased cohort of 131 uniformly treated precursor-B-ALL patients, we determined MRD levels at 42 and 84 days after treatment initiation using RQ-PCR analysis of Ig/TCR rearrangements. Based on these levels, patients were divided into three groups: MRD-Low (MRD-L), MRD-Medium (MRD-M) and MRD-High (MRD-H). IKZF1 alterations at diagnosis were determined using multiplex ligation-dependent probe amplification and genomic sequencing. We confirmed the strong prognostic significance of MRD classification, which was independent of IKZF1 status. Importantly, in the large MRD-M group (n=81; 62% of patients) containing 46% of the relapsed patients, IKZF1 alteration status identified 8 out of 11 relapsed patients (72%). The 9 year relapse-free survival (RFS) for IKZF1 mutated patients in this MRD-M group was 27% compared to 96% for patients wild-type for IKZF1 (P<0.001). Based on these results, we defined a new parameter integrating both MRD and IKZF1 status. The favorable risk group included patients classified as MRD-L or MRD-M with IKZF1 wild-type (n=104; 5 relapses), whereas the high risk group consisted of MRD-H patients or MRD-M patients with IKZF1 alterations (n=27; 19 relapses). This parameter showed stronger prognostic value than each of the established risk factors alone (Hazard Ratio[95%CI]: 24.98[8.29-75.31]). Importantly, whereas MRD and IKZF1 status alone identified only 46% and 54% of relapses, respectively, their integrated use allowed prediction of 79% of all relapses with 93% specificity. In conclusion: The use of a new parameter integrating MRD and IKZF1 status results in an unprecedented sensitivity in upfront relapse prediction and has a high potential for future risk stratification, particularly for patients originally classified as non-high-risk, such as the large group of MRD-M patients.