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WHO Classification of Tumours
T Lymphoblastic leukaemia/lymphoma
Tumours of haematopoietic and lymphoid tissues


Definition

T lymphoblastic leukaemia/ lymphoblastic lymphoma is a neoplasm of lymphoblasts committed to the T-cell lineage, typically composed of small to medium-sized blast cells with scant cytoplasm, moderately condensed to dispersed chromatin and inconspicuous nucleoli, involving bone marrow (BM) and blood (T-acute lympho­blastic leukaemia, T-ALL) or presenting with primary involvement of thymus, nodal or extranodal sites (T-acute lymphoblastic lymphoma, T-LBL). By convention, the term lymphoma is used when the process is confined to a mass lesion with no or minimal evidence of peripheral blood (PB) and BM involvement. With extensive BM and PB involvement, lympho­blastic leukaemia is the appropriate term. If the patient presents with a mass lesion and lymphoblasts in the BM, the distinction between leukaemia and lymphoma is arbitrary. For many treatment protocols, a figure of >25% BM blasts is used as the threshold for defining leukaemia. In contrast to myeloid leukaemias, there is no agreed-upon lower limit for the percentage of blasts required to establish a diagnosis of ALL. In general, the diagnosis should be avoided when there are <20% blasts.

> Related Topics
Mixed phenotype acute leukaemia, T/myeloid
T-cell prolymphocytic leukaemia
Natural killer (NK) cell lymphoblastic leukaemia/lymphoma
Introduction: Classification of lymphoid neoplasms