Precursor T-lymphoblastic lymphoma/leukemia is a neoplasm of lymphoblasts committed to the T-cell lineage, typically composed of small to medium-sized blasts with scant cytoplasm, moderately condensed to dispersed chromatin and indistinct nucleoli, variably involving bone marrow and blood (T-cell acute lymphoblastic leukemia), thymus, and/or lymph nodes (T-cell lymphoblastic lymphoma).¹

Clinically, a case is defined as lymphoma if there is a mediastinal or other mass and <25% blasts in the bone marrow and as leukemia if there are >25% bone marrow blasts, with or without a mass.¹ However, the threshold of 25% blasts in the bone marrow is not firmly defined by the World Health Organization (WHO).¹

Patients with ataxia telangiectasia are at increased risk for development of precursor T-cell lymphoblastic lymphoma, but the ATM gene has not been implicated in sporadic T-cell precursor neoplasia.¹

Precursor T-cell lymphoblastic lymphoma is rare, accounting for 1% to 2% of all non-Hodgkin lymphomas.¹ The neoplasm occurs most frequently in late childhood, adolescence, and young adulthood, with a male predominance.¹ Patients usually present with a bulky anterior mediastinal mass, associated with pleural or pericardial effusions, superior vena cava syndrome, and tracheal obstruction. The tumor typically involves the thymus and often mediastinal, cervical, supraclavicular, or axillary lymph nodes. The bone marrow and peripheral blood are involved in the majority of the cases.¹ Central nervous system (CNS) involvement is also common, but abdominal involvement (liver and spleen) is unusual.^1,2,3

Grossly, the tumor often presents as a solid mass lesion with grayishwhite fleshy cut surface involving the thymus or mediastinal lymph nodes. Invasion into the adjacent pericardium and pleura is sometimes found.