Myeloid/natural killer cell blast crisis representing an additional translocation, t(3;7)(q26;q21) in Philadelphia-positive chronic myelogenous leukemia

We encountered a patient in blast crisis (BC) with chronic myelogenous leukemia (CML) who showed immunophenotypic features similar to those previously described in acute myeloid/natural killer (NK) cell precursor leukemia. The blasts were positive for CD7, CD33, CD34, and CD56. Cytogenetic analysis disclosed a Philadelphia chromosome (Ph) and t(3;7)(q26;q21). Molecular analysis did not detect any EVI1/CDK6 chimeric transcript generated by t(3;7)(q26;q21), but did indicate overexpression of EVI1, which occurs frequently in progression to myeloid BC in CML. Three cases of myeloid/NK cell precursor BC in CML have been reported, but this case is the first to present with Ph and EVI1 abnormality. These observations suggested that a myeloid/NK cell precursor might have been involved in the Ph-positive clone and have been a target for blastic transformation of CML, although EVI1 expression is not specific for transformation to BC from myeloid/NK lineage.