Early treatment sensitivity in childhood acute lymphoblastic leukemia is associated with gain of chromosome 21.

5271 Acute lymphoblastic leukemia (ALL) is the most common malignancy in childhood. In vivo response to initial therapy, as assessed by determination of minimal residual disease at 5 and 12 weeks of treatment, has evolved as the strongest prognostic factor in pediatric ALL patients treated according to the BFM regime. In this study, ten patients with a poor treatment response (MRD load > 10-3 at week 12, MRD-high risk, HR), five treatment-sensitive patients (no measurable MRD at weeks 5 and 12, MRD-standard risk, SR) and three patient with an intermediate treatment sensitivity (any MRD positivity at week 5, MRD load