A high-grade malignant lymphoma composed of a diffuse, relatively uniform proliferation of cells with round or convoluted nuclei and scanty cytoplasm. The cells are cytologically similar to the lymphoblasts seen in acute lymphocytic leukemia, and in some cases, the disease may evolve into a leukemic phase morphologically indistinguishable from acute T-lymphocytic leukemia (LEUKEMIA, T-CELL, ACUTE). Lymphoblastic lymphoma represents approximately one-third of the cases of non-Hodgkin's lymphomas in children and 5% of the cases in adults. It is more prevalent in males.