Case: Extramedullary blast crisis (EBC) is a special kind of blast crisis of chronic myelogenous leukemia (CML). It is more likely to be misdiagnosed as lymphoma when EBC cells are of lymphoid cell lineage and lymphadenopathy is the only symptom before the final diagnosis. In this study, we presented a patient with an unusual presentation of CML transformation as a rapid growth of generalized lymphadenopathy that appeared 5 months after the initial diagnosis
of CML. The patient underwent the left supraclavicular lymph node biopsy and repeat bone marrow aspiration. The revealed CD3+, terminal deoxynucleotidyl transferase (TdT)+, CD5+, CD23+, myeloperoxidase (MPO)-, CD20-, cyclin D1-, CD10-, which was consistent with the diagnosis of T-cell lymphoblastic lymphoma (T-LBL). Fluorescence in situ hybridization (FISH) verified the BCR-ABL rearrangement, and T-cell EBC of CML was finally diagnosed. Our report suggested that the FISH was necessary to distinguish isolated lymphoid extramedullary blast crisis from secondary NHL in CML.