Improved Post-Induction Chemotherapy Does Not Abrogate Prognostic Significance of Minimal Residual Disease (MRD) for Children and Young Adults with High Risk Acute Lymphoblastic Leukemia (ALL). A Report From Children's Oncology Group (COG) Study AALL0232

Abstract 1440 Improved Post-Induction Chemotherapy Does Not Abrogate Prognostic Significance of Minimal Residual Disease (MRD) for Children and Young Adults with High Risk Acute Lymphoblastic Leukemia (ALL). A Report from Children's Oncology Group (COG) Study AALL0232. Minimal residual disease is one of the strongest prognostic factors in pediatric ALL. COG AALL0232 was a phase 3 randomized trial for patients 1–30 years old with newly diagnosed NCI HR B precursor ALL that used a 2×2 factorial study design comparing dexamethasone (DEX) versus(vs.) prednisone(PRED) during induction, and high dose methotrexate (HD-MTX) vs. Capizzi methotrexate (C-MTX) during interim maintenance 1(IM-1). We previously reported improved event-free survival (EFS) for patients receiving HD-MTX vs. C-MTX (J Clin Oncol 29: 6s, 2011) and for DEX vs. PRED among patients <10 years old randomized to HD-MTX(J Clin Oncol 29: 586s,2011). MRD was measured by 6 color flow cytometry in two central labs (MJB and BLW) to a level of sensitivity of 0.01% at end induction. Patients with >=0.1% MRD at end induction, as well as patients with morphologic slow early response or specific adverse genetic features received intensified therapy including IM-2 and a second delayed intensification, and then had MRD determined at end consolidation, (about 13 weeks post diagnosis). End induction MRD > =0.01% was highly predictive of inferior outcome, though patients with 0.1–1% MRD who received intensive therapy had very low rates of early relapse and a much higher rate of late relapse. 5 year EFS for end-induction MRD positive (>=0.01%) patients was 63±5% vs. 86±2% for MRD negative patients. However, patients who were MRD positive at end induction who became negative by end consolidation had improved 5y EFS of 79±9%(n=136) compared to 52±14% for those who remained MRD positive(n=52) (p=.0012). Both end induction MRD positive and negative patients benefitted from HD-MTX vs. C-MTX, though the effect was small and did not reach statistical significance for MRD positive patients. By contrast, end-induction MRD was highly predictive of outcome for patients receiving either HD-MTX or C-MTX. 5 y EFS as a function of MRD status and IM regimen.End induction MRDCapizziHDMTXP value<.01%84 ± 3%88 ± 2%.04>.01%59 ± 6%67 ± 7%.12P value<.0001<.0001 End induction MRD negative patients <10y receiving DEX had better outcome than those getting PRED (5 y EFS 92±3% vs. 87±4% P=.027) while MRD positive patients or those>10y showed no difference. However, DEX patients <10y if anything had a slightly higher rate of end induction MRD positivity than those given PRED (22% vs. 17%, p=.073). In multivariate analysis, end consolidation MRD was the most powerful prognostic factor for the small subset of patients in whom this was assessed. Excluding this, end induction MRD was the most significant variable; age, white blood cell count, day 15 marrow morphology and HD-MTX vs. C-MTX were also significant. We conclude that MRD remains the most powerful prognostic factor even in the context of improved therapy. Additionally, for those patients who were MRD positive at end induction, achieving MRD negative status by end consolidation improved outcome significantly. The higher frequency of MRD in younger patients receiving DEX calls into question the validity of using end induction MRD as a surrogate for outcome when testing novel interventions during induction therapy. Disclosures: Borowitz: BD Biosciences: Research Funding. Wood:BD Biosciences: Research Funding.