Abstract
T-cell acute lymphoblastic leukemia/lymphoma (T-ALL/LBL) is a rare and aggressive leukemia. Philadelphia chromosome-positive cytogenetic abnormality is most common in CML. It is difficult to differentiate between de novo Ph+ T-ALL/LBL and T-cell lymphoblastic crises of CML. We present a case of adult Ph+ T-ALL/LBL with a likely history of antecedent CML. Initially thought to be a case of chronic-phase CML, a diagnostic quandary led to the pursuit of a lymph node biopsy that established the diagnosis of Ph+ T-LBL or T lymphoblastic blast crisis of CML, a clinical presentation extremely rare and only the second of its kind from our review of the literature. The patient was treated with an intensive chemotherapy regimen for over a year due to persistent minimal residual disease (MRD) positivity indicating aggressive disease.