Microtype BCR/ABL rearrangement is extremely rare and has been known to be associated with neutrophilic chronic myeloid leukemia (N-CML). However, there is more to be understood regarding this phenotype. We report a case of atypical CML that exhibited micro BCR/ABL rearrangement with predominant thrombocytosis. Our patient showed thrombocytosis (1,464×10⁹/L) and megakaryocytosis in the peripheral blood and bone marrow. However, neither leukocytosis nor neutrophilia was observed (white blood cells (WBC), 5.02×10⁹/L neutrophils, 45%). Bone marrow aspirate revealed increased cellularity: 12% basophils, 6% eosinophils, and 9% blasts. The 46,XX,t(9;22)(q34;q11.2),i(17q) chromosome complement was observed in 4 of 20 metaphase cells, and standard BCR/ABL fusion signals were observed in 10% of interphase cells on fluorescence in situ-hybridization (FISH) analysis. Reverse transcriptase- polymerase chain reaction (RT-PCR) was used to acquire the BCR/ABL fusion transcript, the identity of which was confirmed via sequence analysis. Hematologic remission was achieved 2 months after imatinib therapy initiation, and molecular remission was achieved 2 months after hematologic remission. The patient is currently undergoing regular follow-up visits and is in good health. However, further long-term follow up is warranted. The incorporation of imatinib into therapeutic strategies may be further established through the study of more cases of micro BCR/ABL

Keywords: Atypical CML, Micro BCR/ABL, ET, Imatinib