Small, abnormal B lymphoid blast populations in chronic myelogenous leukemia at diagnosis: Does this finding indicate an accelerated course?

BACKGROUND: The 2008 WHO is not specific regarding subclassification of chronic myelogenous leukemia (CML) with less than 20% abnormal B lymphoid blasts (ABLB), and suggests patients with ABLB often show rapid progression (Swerdlow, 2008). Recent studies have shown variable outcomes when small abnormal B cell populations are seen by flow cytometry (El Rassi et al., Cancer 2015; 121:872-875; Vrotsos et al., Cytometry B Clin Cytom 2015).

METHODS: The hematopathology database was searched (7.4-year period), and patients identified through routine clinical study, who were BCR-ABL1 positive CML and had an ABLB of less than 20%. Flow cytometric (FC) and histologic data was evaluated to determine immunophenotypic abnormalities, immunohistochemical patterns, and percentage of ABLB, hematogones, and mature B cells.

RESULTS: Seven patients with CML and ABLB identified by FC studies were found, five of which also had available histologic material to review. ABLB by FC ranged from 0.006% to 3.4%, typically demonstrated an immunophenotype with increased CD10, increased CD19, and decreased CD38, without myeloid antigens, abnormalities similar to that reported previously (Vrotsos et al., Cytometry B Clin Cytom 2015). The ABLB population was found only in diagnostic samples and always with more numerous hematogones. By immunohistochemistry, three of five patients showed ≥10% TdT positive cells. All patients showed a response to tyrosine kinase inhibitor therapy, and no patients progressed to clinical lymphoid blast phase.

CONCLUSIONS: Immature B cells, occasionally including a small subset with an abnormal phenotype can be observed in chronic phase CML at diagnosis. We believe an approach incorporating clinical data, cytogenetic/molecular findings, and morphologic evaluation may be helpful when determining the best management of CML patients at diagnosis if small ABLB populations are identified by FC. © 2016 Clinical Cytometry Society.