A tumor in the cavity which separates the lungs and contains the heart, the large blood vessels, the trachea, the thymus, and connective tissues.For leukemias, chemotherapy followed by radiation is the treatment of choice.
The major extramedullary disease manifestations were a mediastinal mass in 8% of patients, nodal involvement (without mediastinal involvement) in 36%, liver and spleen enlargement (organ palpable more than 4 cm below the costal margin) in 31% and 27%, respectively, and CNS involvement in 2.5%.