Clinical significance of early T-cell precursor acute lymphoblastic leukaemia: results of the Tokyo Children's Cancer Study Group Study L99-15

Summary Early T‐cell precursor acute lymphoblastic leukaemia (ETP‐ALL) is a recently identified subtype of T‐ALL with distinctive gene expression and cell marker profiles, poor response to chemotherapy and a very high risk of relapse. We determined the reliability of restricted panel of cell markers to identify EPT‐ALL using a previously classified cohort. Then, we applied the cell marker profile that best discriminated ETP‐ALL to a cohort of 91 patients with T‐ALL enrolled in the Tokyo Children’s Cancer Study Group L99‐15 study, which included allogeneic stem cell transplantation (allo‐SCT) for patients with poor prednisone response. Five of the 91 patients (5·5%) met the ETP‐ALL criteria. There were no significant differences in presenting clinical features between these and the remaining 86 patients. Response to early remission induction therapy was inferior in ETP‐ALL as compared with T‐ALL. The ETP‐ALL subgroup showed a significantly poorer event‐free survival (4‐year rate; 40%) than the T‐ALL subgroup (70%, P = 0·014). Of note, three of four relapsed ETP‐ALL patients survived after allo‐SCT, indicating that allo‐SCT can be effective for this drug‐resistant subtype of T‐ALL.