ETV6-RUNX1-positive B precursor acute lymphoblastic leukemia (B-ALL) is a common subtype of pediatric B-ALL that has shown excellent outcomes in contemporary clinical trials for pediatric B-ALL. Examinations of the possibility of reducing therapeutic intensity may thus be explored. This prospective study examined outcomes in 205 pediatric patients with ETV6-RUNX1-positive B-ALL uniformly treated following the Japan Association of Childhood Leukemia Study Group (JACLS) ALL-02 protocol. The JACLS ALL-02 protocol does not employ minimal residual disease detected by polymerase chain reaction (PCR-MRD)-based risk stratification; however, 4-year event-free survival (EFS) and overall survival (OS) were 94.4 ± 1.6 and 97.5 ± 1.1%, respectively. In particular, 92 of 205 (44.9%) patients were successfully treated with a less intensive regimen involving only two cycles of high dose methotrexate and one course of re-induction therapy comprising vincristine, l-asparaginase (L-asp), pirarubicin, and prednisolone. Multivariate analysis revealed that discontinuation of L-asp and poor response to prednisolone was, respectively, associated with poor EFS (HR 6.3; 95% CI 1.3–27.0) and OS (HR 17.5; 95% CI 2.3–130), suggesting that the majority of ETV6-RUNX1-positive B-ALL cases may be cured by a less-intensive chemotherapy regimen if the risk stratification system including PCR-MRD monitoring and insufficient use of L-asp is avoided.
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