T-lymphoblastic leukemia/lymphoma, previously labeled precursor T-lymphoblastic leukemia/lymphoma is a form of lymphoid leukemia and lymphoma in which too many T-cell lymphoblasts are found in the blood, bone marrow, and tissues, particularly mediastinal lymph nodes. Labeling as leukemia or lymphoma depends on which feature is more pronounced in a given situation, but has no biological or treatment implication.