Case Report: Pediatric Philadelphia chromosome-positive T-lymphoblastic leukemia relapsing as chronic-phase CML after...

Philadelphia chromosome (Ph)-positive T-lymphoblastic leukemia (T-ALL) is exceptionally rare. Distinguishing de novo Ph-positive T-ALL from T-lymphoid blast-phase chronic myeloid leukemia (BP-CML) can be highly challenging, yet this distinction has important therapeutic and prognostic implications. We report a pediatric patient initially diagnosed with de novo Ph-positive T-ALL who subsequently developed CML following treatment discontinuation.

A 14-year-old boy presented with fever, leukocytosis, and generalized lymphadenopathy. Bone marrow examination revealed 81% blasts, and flow cytometric immunophenotyping confirmed T-ALL (cytoplasmic CD3⁺ CD5⁺ CD7⁺⁺). Conventional cytogenetic analysis revealed a karyotype of 49,XY,-7,+8,t(9;22)(q34;q11.2),+15,+19,+mar[3], and real-time quantitative reverse-transcription polymerase chain reaction detected a b3a2 BCR::ABL1 fusion transcript. A diagnosis of de novo Ph-positive T-ALL was rendered, and the patient achieved complete remission following induction chemotherapy with VICP (vincristine, idarubicin, cyclophosphamide, prednisone) plus imatinib. The patient declined both allogeneic hematopoietic stem cell transplantation and escalation to a second-generation tyrosine kinase inhibitor (TKI). After self-discontinuing imatinib without medical advice for approximately 18 months, he developed CML.

This case highlights the diagnostic challenge of distinguishing de novo Ph-positive T-ALL from T-lymphoid BP-CML at initial presentation, particularly in pediatric patients. Accurate classification is essential because it has important implications for therapeutic decision-making and long-term management in the TKI era. The subsequent development of CML following TKI discontinuation strongly supports that the initial presentation represented lymphoid BP-CML rather than de novo Ph-positive T-ALL. This observation further underscores the importance of sustained TKI therapy and adherence in preventing disease recurrence and optimizing long-term clinical outcomes.