Eosinophilic blast crisis in a case of chronic myeloid leukaemia

A case of typical chronic myeloid leukaemia (CML) is described, of which the terminal blast crisis was characterized by an impressive proliferation of atypical eosinophils and by the simultaneous complete deficiency of neutrophilic myeloperoxidase. Since eosinophilic cells preserved a strong peroxidase positivity, a high number of immature non-granular eosinophilic precursors could be recognized among the leukaemic blast cells, thus supporting the diagnosis of eosinophilic blast crisis of CML.