Abstract Background Chronic myeloid leukemia (CML) presenting in blast crisis (BC) is uncommon in the era of tyrosine kinase inhibitor (TKI) treatment, and T‐lymphoblastic BC is exceptionally rare. We report a case of T‐lymphoid BC presenting with extreme hyperleukocytosis. Case: A 37‐year‐old woman with previously diagnosed chronic phase CML who had declined therapy presented with dyspnea and constitutional symptoms. She was found to have diffuse lymphadenopathy and a markedly elevated white cell count (WCC) of 729 × 10 9 /L with 24% blasts. Bone marrow biopsy showed T‐lymphoblastic leukemia, BCR::ABL1 fusion (p210), and a RUNX1 gene mutation as well as an IKZF1 gene mutation. Staging revealed extensive nodal, splenic, renal, and ocular involvement. She underwent cytoreduction with hydroxyurea, prednisone, and dasatinib, followed by HyperCVAD induction. She achieved complete remission and proceeded to a sibling‐donor allogeneic stem cell transplant. A bone marrow biopsy 100 days after transplant showed complete remission without MRD assessed by PCR and flow cytometry. At 6 months post‐transplant, she remains disease‐free. Discussion T‐lymphoid BC in CML is exceedingly rare, with limited knowledge of disease characteristics, molecular features, prognosis, and treatment outcomes. This case highlights the importance of early recognition, comprehensive molecular workup, and aggressive therapy. Despite historically poor outcomes, aggressive induction with BCR‐ABL1 kinase inhibition followed by transplant may offer durable disease control. Trial Registration The authors have confirmed clinical trial registration is not needed for this submission.
Somasundaram et al. (2026) studied this question.