Practical approaches to the diagnosis and differential diagnosis of T-lymphoblastic leukemia/lymphoma.

T-lymphoblastic leukemia/lymphoma is a malignant neoplasm derived from T-cell precursors. These neoplasms can present initially as acute lymphoblastic leukemia (ALL) involving bone marrow or lymphoblastic lymphoma (LBL) involving lymph nodes, mediastinum or other extramedullary sites. Bone marrow and extramedullary tissue involvement frequently coexist. In this review, we begin with a short review of the clinical and morphologic features of ALL/LBL. We then focus on the immunophenotypic features of T-ALL/LBL. We delineate lineage-defining T-cell markers and immaturity-associated markers for the diagnosis and summarize immunophenotypic subtypes of T-ALL/LBL. Lastly, we discuss the differential diagnosis of T-ALL/LBL and address the challenges in distinguishing this neoplasm from acute undifferentiated leukemia, acute myeloid leukemia with minimal differentiation, mixed-phenotype acute leukemia, mature T-cell neoplasms, NK-cell neoplasms, T-lymphoblastic phase of chronic myeloid neoplasm, thymoma, indolent T-lymphoblastic proliferation, and blastic plasmacytoid dendritic cell neoplasm.