Hodgkin lymphoma, or Hodgkin disease, is named for Thomas Hodgkin, M.D., who determined it to be a new disease in 1832. All other types of lymphoma are of the non-Hodgkin type. The two types are similar and usually can be distinguished only by examining the cancerous tissue under a microscope, says the ACS. Hodgkin lymphoma makes up less than 1% of all cancer cases in this country; non-Hodgkin lymphoma makes up about 4%.

Other types of cancer can spread to the lymphatic system, but lymphomas are the most common type of cancer that arise there. The lymphatic system is a key part of the body's immune system. It is made up of lymph vessels, which carry a fluid called lymph throughout the body. Lymph contains white blood cells called lymphocytes, which are special cells that fight infections. The lymphatic system also includes lymph nodes scattered throughout the body. Other parts of the body that make up the lymphatic system are the tonsils, spleen, bone marrow, and thymus. Lymph tissue can also be found in many other organs, including parts of the digestive tract. The lymphatic system works to filter out bacteria, viruses, and other harmful substances from the body.

NHL occurs most often in lymph nodes in the chest, neck, abdomen, tonsils, and skin. But NHL also can start in the spleen or other lymph organs, or in lymph tissue found in other organs. Lymphocytes circulate throughout the body via the lymphatic system and bloodstream. Any abnormal lymphocytes can travel on these same pathways. Some NHLs stay in one spot in the body, but many have spread elsewhere by the time lymphoma is diagnosed.

Lymph nodes increase in size when they fight an infection, the ACS says. These nodes are often tender to touch. An enlarged lymph node is usually not serious, especially during an infection such as a sore throat or a cold. But an enlarged lymph node is also the most common sign of lymphoma, the ACS says.

The risk of developing NHL increases with age, according to the ACS. More than 95% of cases occur in adults. About 70,000 Americans are diagnosed with NHL each year. Overall, it is more common in men than in women, although some types are more common in women, and more common in whites than other ethnic groups.

Lymphomas are not contagious. Although the exact causes of NHL are not known, researchers have identified several possible risk factors besides advancing age. They include working with or being exposed to chemicals such as pesticides, fertilizers, or solvents; being exposed to high doses of radiation; having the Epstein-Barr virus, the human T-lymphotropic virus type 1, HIV, or certain other infections; having a family member with NHL; having certain immune system problems; or having an organ transplant.

Other symptoms can include enlarged lymph nodes, fever, and night sweats. Fever may occur only at night for several days, and then disappear for a period, then return. The most common initial sign of NHL is the enlargement of one or more lymph nodes. This enlargement usually is painless.

Treatment is tied to the type and grade of the lymphoma and the extent of the disease, says the ACS. A low-grade form may just be monitored, with no treatment until the disease begins to cause problems. Chemotherapy, radiation therapy, and immunotherapy may be used for more aggressive forms of NHL, where starting treatment early is more more important. Bone marrow or stem cell transplants may be used in some cases.