Isolated Central Nervous System blast crisis in chronic myeloid leukemia: A rare case report

Chronic myeloid leukemia (CML) is a triphasic myeloproliferative neoplasm, characterized by the presence of the Philadelphia chromosome Ph+ (BCRABL fusion gene- t(9:22)), and most cases of CML manifest in the chronic phase with a high granulocyte count, while 5-10% progress to accelerated or blast crisis. Infiltration of the central nervous system as the only site of extramedullary blast crisis without bone marrow involvement is uncommon and deserves scrutiny. In such cases, a blast crisis could present with either myeloid or lymphoid infiltration, resulting in acute myeloid leukemia or acute lymphoid leukemia, respectively. Imatinib mesylate has promising activity in patients with Ph+ acute leukemias; however, its CNS penetration is poor. We report a 43-year-old male with CML-CP who developed isolated CNS blast crisis with an Early T-cell Precursor Acute Lymphoblastic Leukemia (ETP-ALL) phenotype, and discuss the diagnostic and therapeutic approach.