Children's Oncology Group (COG) AALL0434: Successful Disease Control without Cranial Radiation in Newly Diagnosed T Lymphoblastic Lymphoma (T-LL)

Background: COG AALL0434 evaluated the safety and efficacy of a multi agent chemotherapy backbone containing Capizzi based methotrexate/pegaspargase in newly diagnosed T-LL patients. High-risk patients were randomized to receive the COG augmented BFM (ABFM) regimen with or without Nelarabine. This was part of a larger trial including T-Lymphoblastic Leukemia (T-ALL) patients featuring a 2 x 2 pseudo-factorial randomization at the end of induction using the COG ABFM regimen with a randomization of Capizzi MTX/pegaspargase (C-MTX) verses high dose MTX and a randomization with or without Nelarabine (Nel). Methods: AALL0434 enrolled 277 patients with T-LL (2010-2014). Patients were assigned to two risk categories based upon the degree of bone marrow involvement at diagnosis: (≥1%, High Risk, <1% Standard Risk), and the ability to achieve at least a partial response at the end of induction. Patients with prior steroid treatment were assigned to the high risk group. Both groups were treated using the ABFM C-MTX regimen. High-risk patients were randomized to receive or not receive six, 5-day courses of Nel 650 mg/m2/day. No patients received prophylactic cranial radiation and CNS3 patients were ineligible. Response criteria included, Complete Response (CR): disappearance, Complete Response unconfirmed (CRu): >75% reduction, Partial Response (PR): >50% reduction, of all measurable disease, all without new lesions. Results: At the end of induction, 98.9% of the evaluable patients achieved at least a partial response (30.7% CR, 34.7% CRu, 33.5% PR). For all T-LL patients, the 4-year event free survival (EFS) and overall survival (OS) were 87.0 +/- 2.1% and 90.0+/-1.8%. The 4-year Disease Free Survival (DFS) from end of induction was 90.0+/- 2.1%. There was no difference in DFS observed between the high risk and standard risk groups, (p=0.25) or by treatment regimen (p=0.31). Nel did not show an advantage for high-risk T-LL patients, with 4-year DFS 85.0 +/- 5.6% with Nel (N=60) vs 89.0 +/- 4.7% without Nel (N=58) (p=0.28). Neither stage nor tumor response at the end of four weeks of induction therapy resulted in differences in EFS (p= 0.34 and p= 0.22, respectively). Minimal detectable disease (MDD) of the bone marrow at diagnosis (<0.1%, 0.1-0.99%, >1.0%), used to establish the risk assignment for this trial, failed to demonstrate thresholds at diagnosis that resulted in differences in EFS (p=0.27). Relapse involving the CNS only occurred in 4 patients (1.4%). Overall toxicity and neurotoxicity was acceptable and not significantly different than that experienced from the ALL cohort. There was one observed second malignancy and 5 deaths not from progressive disease. Conclusion: COG AALL0434 produced excellent outcomes in one of the largest trials ever conducted for patients with newly diagnosed T-LL. The COG ABFM regimen with C-MTX provides excellent disease control regardless of stage, or the degree of disease involvement of the bone marrow at diagnosis. Nelarabine did not show an improvement in the outcome, although the trial was underpowered to address this specific question. Disclosures Teachey: Amgen: Consultancy; La Roche: Consultancy. Bollard:Torque: Honoraria, Membership on an entity's Board of Directors or advisory committees; Cellectis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Neximmune: Honoraria, Membership on an entity's Board of Directors or advisory committees.