Hodgkin's disease is a type of lymphoma. Lymphomas are cancers that develop in the lymphatic system, part of the body's immune system. The job of the lymphatic system is to help fight diseases and infection.

The lymphatic system includes a network of thin tubes that branch, like blood vessels, into the tissues throughout the body. Lymphatic vessels carry lymph, a colorless, watery fluid that contains infection-fighting cells called lymphocytes. Along this network of vessels are groups of small, bean-shaped organs called lymph nodes that filter the lymph as it passes through the nodes. Clusters of lymph nodes are found in the underarm, groin, neck and abdomen. Other parts of the lymphatic system are the spleen, thymus, tonsils and bone marrow.

Like all types of cancer, Hodgkin's disease affects the body's cells. Healthy cells grow, divide and replace themselves in an orderly manner. This process keeps the body in good repair. In Hodgkin's disease, cells in the lymphatic system grow abnormally and can spread to other organs. As the disease progresses, the body is less able to fight infection.

Hodgkin's disease is rare. It accounts for less than 1 percent of all cases of cancer in this country. It is most often seen in young people aged 15 to 34 and in people over the age of 55. Other cancers of the lymphatic system are called non-Hodgkin's lymphomas; information about these can be found in a separate section of this Web site.