MSH: A leukemia/lymphoma found predominately in children and young adults and characterized LYMPHADENOPATHY and THYMUS GLAND involvement. It most frequently presents as a lymphoma, but a leukemic progression in the bone marrow is common.,NCI: Acute lymphoblastic leukemia of T-cell origin. It comprises about 15% of childhood cases and 25% of adult cases. It is more common in males than females. (WHO, 2001),NCI: An aggressive (fast-growing) type of leukemia (blood cancer) in which too many T-cell lymphoblasts (immature white blood cells) are found in the bone marrow and blood.