Precursor T-cell acute lymphoblastic leukemia

A rare acute lymphoblastic leukemia characterized by a neoplasm of lymphoblasts committed to the T-cell lineage, involving bone marrow and blood. A value of >25% bone marrow blasts may be used to define leukemia (as opposed to lymphoma) in cases with the presence of a mass lesion in addition to bone marrow involvement. Patients typically present with leukocytosis, and frequently with a large mediastinal or other tissue mass. Lymphadenopathy and hepatosplenomegaly are common.