T-cell blast crisis of chronic myelogenous leukemia manifesting as a large mediastinal tumor

We report an unusual case of T-cell blast crisis of chronic myelogenous leukemia (CML) with a clinical presentation more typical of de novo T-cell lymphoblastic lymphoma. The patient was a 32-year-old man who presented with acute superior vena cava syndrome 19 months after an initial diagnosis of CML and 5 months after allogeneic bone marrow transplantation. The tumor was composed of primitive lymphoid cells expressing CD2, CD3, CD4, CD5, CD7, CD8, and CD10. Although the clinical features were more typical of acute lymphoblastic leukemia/lymphoma, fluorescence in situ hybridization analysis showed the bcr-abl fusion gene within blastic tumor cells. This finding confirmed that the mass represented a blastic transformation of CML. We use the unusual features of the current case and the previous reports to suggest that the development of T-cell blast crisis of CML is dependent on the presence of both marrow and extramedullary disease and a mechanism to evade apoptosis.