Detection of abnormalities in B‐cell differentiation pattern is a useful tool to predict relapse in precursor‐B‐ALL

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Abstract
Immunophenotypic investigation of minimal residual disease (MRD) has traditionally been based on the investigation of phenotypic aberrants at diagnosis to be used later as a target for MRD detection. This approach has several shortcomings (it is only applicable to patients with aberrant phenotypes, requires a diagnostic sample, and is patient‐specific) and therefore a search for simpler alternatives is warranted. The present study is based on the hypothesis that in precursor‐B‐ALL patients the persistence of residual leukaemic cells may induce abnormalities in the precursor‐B‐cell compartment in bone marrow (BM) and these could be used as a criteria to predict relapse. These abnormalities may include: (1) the presence of an increase in the frequencies of immature B cells (CD34+/CD19+ or CD20−/CD19+) or (2) the existence of an altered B‐cell differentiation pathway due to a blockade or to the presence of B cells outside the normal pathway. A total of 180 BM samples from 45 consecutive precursor‐B‐ALL patients who achieved morphological complete remission (CR) were analysed by multiparametric flow cytometry. Our results show that a significant increase in immature B‐cell subsets or an altered B‐cell differentiation predicts a high relapse rate (P < 0.01) and a shorter disease‐free survival (P < 0.01). Moreover, abnormalities in either of these two criteria detected at specific time points during follow‐up (end of induction, maintenance, or after treatment) were associated with a significantly shorter disease‐free survival (P < 0.01). In summary, the investigation of abnormalities in B‐cell differentiation is a relatively simple and cheap approach for predicting relapse in precursor‐B‐ALL patients.