[Extramedullary blast crisis limited to the lymph nodes in chronic myeloid leukemia with a T/myeloid mixed phenotype].

Blast crisis (BC) in chronic myelocytic leukemia (CML) typically presents with increased blasts in the bone marrow, showing either myeloid or B-lymphoid phenotypes. We report a rare case of CML-BC with a T/myeloid mixed phenotype localized to the lymph nodes. An 80-year-old woman presented with right axillary lymphadenopathy. PET-CT revealed multiple enlarged lymph nodes. Axillary node biopsy showed proliferation of medium-sized atypical lymphoid-like cells expressing both T-cell and myeloid markers. Both bone marrow and peripheral blood showed no abnormalities. The BCR::ABL1 translocation was detected in both bone marrow and lymph node tissue. Fluorescence in situ hybridization showed positive staining for BCR/ABL1 gene rearrangement. Based on these findings, blast crisis of CML with a T/myeloid mixed phenotype was diagnosed. Following dasatinib therapy, the enlarged nodes regressed. Despite the patient's advanced age, no significant adverse events have been observed during the course of treatment.