Objective. Evaluate the prognostic value of the regression of leukemic cells (LC) rate in the period from the 15th to the 36th day of the induction therapy for survival rates of children with acute lymphoblastic leucosis (B-ALL) receiving treatment according to the ALL-MB-2008 protocol. Using estimates of the rate of the LC regression and of the minimal residual disease (MRD) value on the 36th day of therapy, identify the group of patients at the highest risk of relapsing.

Materials and methods. The study included B-ALL 517 patients aged 1 to 18 years (median age — 4.16 years) lacking translocations t(9;22), t(4;11) the MRD values known on the 15th and 36th day of the induction therapy. The MRD values were determined by the 5—10-color flow cytometry. The studied patients were treated according to the ALL-MB 2008 protocol, therapy was initiated during the period from February 2008 to November 2014.

Results. The study of the LC regression rate in the B-ALL patients in the period from the 15th to the 36th day of the induction therapy demonstrated the prognostic significance of the LC clearance for survival rates of those patients. The decrease in the rate of the LC regression between the 15th to the 36th day of the induction therapy was associated with a statistically significant (p<0.001) decrease of the event-free survival and an increase of relapsing cumulative frequency (p=0.0035). The MRD values study on the 36th day of the therapy and the LC clearance during the period between 15 to 36 days of the induction therapy allowed to separate the patients at the highest risk of relapsing. The lowest event-free survival (55±8%) and the highest relapsing cumulative frequency (39.1±8.0%) were found in patients demonstrating the LC regression slow rate or no LC regression within the 15th to the 36th days of the induction therapy as well as in those having MRD³0.1% on the 36th day of the therapy.