Atypical Chronic Myelogenous Leukemia (aCML), characterized by BCR/ABL1 negative and Ph chromosome-negative, is a rare and aggressive leukemia variant with poor prognosis, and although it does not exhibit the conventional CML indicators, it possesses characteristics such as hyperleukocytosis and dysgranulopoiesis. This evidence concerns the gene BCR and chronic myelogenous leukemia, BCR-ABL1 positive.