Evaluation of Relationship between Minimal Residual Disease (MRD) and Relapse in Childhood Acute Lymphoblastic Leukemia (ALL) Using Quantitative Fluorescent PCR.

Acute leukemia is the most common malignancy in children accounting for approximately one-third of all childhood cancers. Modern treatment protocols lead to complete remission (CR) in a considerable proportion of patients with lymphoproliferative disorders. However, many of these patients ultimately relapse, showing that in spite of clinical CR still significant amounts of residual malignant cells persist. Various protocols like cytogenetic, molecular and immunological techniques that are more sensitive than morphology are increasingly used to assess and quantify minimal residual disease (MRD). These techniques produce different levels of sensitivity allowing detection of MRD between 10^-2 - 10^-6. In this study we have assessed the feasibility of fluorescent PCR in MRD detection and quantification using immunoglobuline heavy chain (IgH) gene rearrangement. Bone marrow samples obtained from 40 patients with precursor-B cell ALL after induction, consolidation, reconsolidation and intensification therapy. Analysis of clonally rearranged IgH gene carried out by CDR3 amplification in presence of an internal competitor with known copy number. After induction therapy 53% of the patients who were considered to be in clinical remission phase still had detectable MRD. After consolidation therapy 43% of the patients were MRD positive. Subsequent to maintenance-2 or intensification therapy still in 30% of patients MRD was observed.