Pediatric T-lymphoblastic Leukemia With an Entirely Mature Immunophenotype: A Prompt and Challenging Diagnosis

Children with T-ALL/LBL require prompt diagnosis and treatment. Flow cytometric analysis of T-lineage and immaturity markers usually leads to a straightforward diagnosis. However, rare cases of T-ALL expressing bright CD45 and lacking expression of immature markers can be a diagnostic conundrum and difficult to differentiate from mature T-cell lymphomas lacking surface CD3 expression or aberrantly expressing immature markers, which affects treatment decisions and prognosis. Here, we summarize the clinical, pathologic, and genetic features of 3 pediatric T-ALL cases with an entirely mature immunophenotype.