Lymphoma is a group of cancers that originate in the lymphatic system. Lymphoma are divided into two major categories: Hodgkin lymphoma and all other lymphomas, called non-Hodgkin lymphomas. About 53 percent of the blood cancers that occur each year are lymphomas. Hodgkin lymphoma will represent about 11.5 percent of all lymphomas diagnosed in 2007. Lymphomas result when a lymphocyte, a type of white blood cells, undergoes a malignant change and begins to multiply, eventually crowding out healthy cells and creating tumors that enlarge the lymph nodes or other parts of the immune system. Lymphomas generally start in lymph nodes or collections of lymphatic tissue in organs like the stomach or intestines. They may involve the bone marrow and the blood in some cases. Lymphomas may spread from one site to other parts of the body. Lymphocytic leukemias originate and are most prominent in the bone marrow and spill over into the blood. They occasionally spread to involve the lymph nodes. About 71,380 people living in the United States will be diagnosed with lymphoma in 2007.