Minimal Residual Disease by Flow Cytometry in Children with Acute Lymphoblastic Leukemia. Single-Center Experience

Minimal residual disease (MRD) allows detection of blasts in patients in morphologically complete remission. Detection of MRD in patients with ALL is an independent risk factor associated with lower event-free survival (EFS).

1) Evaluate MRD in bone marrowaspirateby flow cytometry at days 15 and 33 of induction in children with ALL. 2) Determine MRD association with hematologic features. 3) To correlate MRD association with overall survival (OS) and event-free survival (EFS).

Descriptive, retrospective study. Univariate analysis was performed by T- test for continuous varibles and byχ2or Fisher tests for categorical variables. Survival was estimated with Kaplan Meier method. Regression multiple was used for multivariate analysis. p values < 0.05 were deemed as statistically significant. SPSS 15.0 program was used for the analyses.

From January 2006 to December 2009, 84 patients with newly diagnosed ALL, aged 1 –18 years, were admitted at our institution. They were treated according to ALLIC / BFM / GATLA 2002 protocol. Immunophenotypic studies were performed by standard Four-color flow cytometry (FC) using FACSCalibur BD cytometer, MDR follow up panels were tailored depending on aberrant finding at diagnosis. 300.000–500.000 events were acquired using the CellQuest Pro and Paint -a-gate software for data analysis. MDR status has been defined as positive if at least 30–50 clustered events displaying leukemia –associated immunophenotypic characteristics (0,01%).

The mean age at diagnosis was 7.7 years (r: 2.1–18). Mean follow-up 33.9 months (r: 1–66). 38% were female. Immunophenotype: Pro B 5%, common B 87%, Pre B 2%, and T 6%. Good response to prednisone was achieved by 92% of patients. With regard to risk groups, the distribution was: 28% standard, 55% intermediate and 17% high. MRD at day 15 was evaluable in 66 patients (78%), being positive in 35 of them (45%). MRD at day 33 was evaluable in 75 patients (89%), being positive in 10 (12%).

Positive MRD at day 15 was associated with: increased WBC count at diagnosis, high-risk group, higher relapse rate, lower EFS and OS. Otherwise, positive MRD at day 33 was associated: increased WBC count at diagnosis, T immunophenotype, poor response to prednisone, high risk group, lower EFS and OS.

Our data indicate that positive MRD at days 15 and 33 result an independent variable of poor prognosis in children with ALL.

No relevant conflicts of interest to declare.