Leukemias are disseminated diseases originating in the bone marrow. In principle, leukemic blasts can be found all over the body. The most common places where spreading is found outside the bone marrow are spinal fluid, (CNS leukemia) liver, spleen, lymph nodes, and testicles.
When the lymph nodes in the mediastinum are involved (occurs especially in T-cell leukemia), mediastinal tumors can occur with potential life-threatening compression of respiratory tracts and large veins.
For acute myeloid leukemia, in rare cases, extramedullary tumors (myelosarcoma) are present with or without apparent bone marrow affection. These patients are still treated for acute myeloid leukemia.