Abstract
Differentiating chronic myelogenous leukemia in primary blast crisis (CML-BC) from de novo BCR-ABL1-positive acute myeloid leukemia (AML) is a diagnostic challenge with therapeutic consequences. In our case, a basophilia, the presence of the Philadelphia chromosome in all metaphases and the strict exclusion of molecular hallmarks of AML lead us to retain the diagnosis of CML-BC rather than BCR-ABL1+ AML.