An organ of the body in the upper left portion of the abdomen just under the left side of the diaphragm. It contains clusters of lymphocytes like lymph nodes do and also filters the blood of old or worn out blood cells. It is often affected in leukemia , especially the lymphocytic leukemias, lymphoma, and Hodgkin's disease. Enlargement of the spleen is referred to as "splenomegaly". Removal of the spleen by surgery is referred to as "splenectomy". Removal of the spleen can be done since its function can be performed by other organs such as the lymph nodes and liver.