Normally, your white blood cells (lymphocytes) go through a predictable life cycle. Old lymphocytes die, and your body creates new ones to replace them. But in non-Hodgkin's lymphoma, your body produces abnormal lymphocytes that continue to divide and grow uncontrollably. This oversupply of lymphocytes crowds into your lymph nodes, causing them to swell.
Doctors don't know what exactly causes non-Hodgkin's lymphoma. But researchers believe that activation of certain abnormal genes may be involved in the development of all cancers, including lymphomas.
Lymphocytes exist either as B cells or T cells. B cells fight infection by producing plasma cells, which in turn produce antibodies that neutralize foreign invaders. T cells are involved in killing foreign invaders directly. About 85 percent of non-Hodgkin's lymphomas occur in B cells. The rest arise in T cells.
Non-Hodgkin's lymphoma generally involves the presence of cancerous cells in your lymph nodes, but the disease can also spread to other parts of your lymphatic system. These include the lymphatic vessels, tonsils, adenoids, spleen, thymus and bone marrow. Occasionally, non-Hodgkin's lymphoma involves organs outside of the lymphatic system