Slow disappearance of peripheral blood blasts is an adverse prognostic factor in childhood T cell acute lymphoblastic leukemia: a Pediatric Oncology Group study

The rapidity of response to induction therapy is emerging as an important p rognostic factor in children and adolescents with acute lymphoblastic leuke mia (ALL). We studied the relationship between rapidity of reduction in per ipheral blood blast count and treatment outcome in children with T cell ALL (T-ALL). Initial systemic chemotherapy included prednisone, vincristine, d oxorubicin and cyclophosphamide. A Cox analysis evaluated the correlation b etween the length of time that the peripheral blood absolute blast count (A BC) remained above 1000/mm(3) following the start of treatment and event-fr ee survival (EFS). Data were available for 281 patients. Patients for whom the ABC remained >1000/mm(3) for 3 or more days following administration of intensive therapy had an estimated 5-year EFS of 34.2% (s.e. = 7.2) vs 58. 3% (3.5) for those whose ABC was <1000/mm(3) within 0-2 days, with a hazard ratio (HR) of failure of 2.03 (95% CI = 1.35-3.06, P < 0.001) for the slow er responding patients. Pre-treatment of some type (usually with prednisone ) occurred in 128 patients (average duration 1.7 days). When this was accou nted for, patients with an ABC >1000/mm(3) for 5 or more days following the start of treatment of any kind had a HR for failure of 2.27 (95% CI = 1.38 -3.72, P < 0.001) compared to those responding within 0-4 days. Inclusion o f other clinical and biological factors in a multivariate analysis did not alter the prognostic importance of slower blast clearance. Pediatric patien ts with T-ALL who have a circulating blast count >1000/mm(3) at diagnosis a nd a relatively slower response to initial treatment are at increased risk of treatment failure. Rapidity of response may therefore be a clinically us eful prognostic factor for patients with T-ALL.