acute lymphoblastic leukemia A leukemia/lymphoma found predominately in children and adolescents and characterized by a high number of lymphoblasts and solid tumor lesions. Frequent sites involve LYMPH NODES, skin, and bones. It most commonly presents as leukemia. A neoplasm characterized by abnormalities of the lymphoid cell precursors leading to excessive lymphoblasts in the marrow and other organs. It is the most common cancer in children and accounts for the vast majority of all childhood leukemias. Leukemia with an acute onset, characterized by the presence of lymphoblasts in the bone marrow and the peripheral blood. It includes the acute B lymphoblastic leukemia and acute T lymphoblastic leukemia. Leukemia with an acute onset, characterized by the presence of lymphoblasts in the bone marrow and the peripheral blood. It includes the precursor B lymphoblastic leukemia and precursor T lymphoblastic leukemia. When the disease process is confined to a mass lesion with no or minimal evidence of blood and less than 25% marrow involvement, the diagnosis is lymphoblastic lymphoma; with blood and greater than 25% marrow involvement, ALL is the appropriate term. lymphoid neoplasm