BACKGROUND: Chronic myeloid leukemia (CML) is a clonal myeloproliferative disorder characterized by the Philadelphia chromosome generated by the reciprocal translocation t(9: 22)(q34;q11). CML is usually diagnosed in the chronic phase. Blast crisis represents an advanced phase of CML. Extramedullary blast crisis as the initial presentation of CML with bone marrow remaining in chronic phase is an unusual event. Further, extramedullary blast crisis with T lymphoid/myeloid bilineal phenotype as an initial presentation for CML is extremely unusual.

CASE REPORT: Here, we report the case of a 49-year-old male with rapidly enlarged submandibular lymph nodes. Biopsy specimen from the nodes revealed a characteristic appearance with morphologically and immunohistochemically distinct myeloblasts and T lymphoblasts co-localized in 2 adjacent regions, accompanied by chronic phase of the disease in bone marrow. The presence of the BCR/ABL1 fusion gene within both cellular populations in this case confirmed the extramedullary disease represented a localized T lymphoid/myeloid bilineal blastic transformation of CML. After 3 courses of combined chemotherapy plus tyrosine kinase inhibitor treatment, the mass was completely regressed with a 3-log decrease in BCR/ABL1 transcript from baseline. Five months after the diagnosis, the patient showed diminished vision, hand tremors, and weakness of lower extremities. Flow cytometric immunophenotyping of cerebrospinal fluid revealed the presence of myeloid blasts. An isolated central nervous system relapse of leukemia was identified. Following high-dose systemic and intrathecal chemotherapy, the patient continued to do well.

CONCLUSIONS: The possibility of extramedullary blast crisis as an initial presentation in patients with CML should be considered. Further, an isolated central nervous system blast crisis should be considered if neurological symptoms evolve in patients who have shown a good response to therapy.

Keywords: Blast Crisis, Leukemia, Myelogenous, Chronic, BCR-ABL Positive, Precursor T-Cell Lymphoblastic Leukemia-Lymphoma, Sarcoma, Myeloid