Severe toxicity and poor efficacy of reinduction chemotherapy are associated with overall poor outcomes in relapsed B-cell acute lymphoblastic leukemia: a report from the Children's Oncology Group AALL1331 trial.

Children's Oncology Group AALL1331 utilized an intensive chemotherapy induction (Block 1) based on UK ALLR3 induction for children, adolescents, and young adults with acute lymphoblastic leukemia in first relapse, followed by risk-stratified therapy. High/intermediate-risk patients were subsequently randomized to receive two blocks of chemotherapy or two blocks of blinatumomab followed by a hematopoietic stem cell transplant. Low-risk patients were randomized to chemotherapy or chemotherapy cycles intercalated with three blinatumomab blocks. Patients who had early treatment failure were eligible to receive blinatumomab for up to two salvage cycles. We reviewed Block 1 responses, risk stratification, randomization rates, adverse events, event-free survival and overall survival for all enrolled patients. AALL1331 enrolled 661 patients: 24 died during Block 1 and 42 experienced early treatment failure. Overall, 531/661 (80.3%) attained complete remission with 586 risk-assigned and only 471 were randomized. Of 532 patients with bone marrow involvement, 290 (54.5%) were positive for minimal residual disease (≥0.01%) after Block 1. Grade 3, 4 or 5 adverse events occurred in Block 1 in 44.9%, 24.1%, and 3.6% of patients, respectively, with febrile neutropenia, infections, and sepsis being most frequent. Notably, 190 enrolled patients (28.7%) did not proceed with post-induction therapy, including 115 (17.4%) risk-stratified but not randomized. These patients had dismal survival. More effective and less toxic reinduction strategies are needed for B-cell acute lymphoblastic leukemia in first relapse. Trial registration number: NCT02101853.