Hodgkin's disease is a type of lymphoma. Lymphomas are cancers that develop in the lymph system, part of the body's immune system. The lymph system is made up of thin tubes that branch, like blood vessels, into all parts of the body. Lymph vessels carry lymph, a colorless, watery fluid that contains white blood cells called lymphocytes. Along the network of vessels are groups of small, bean-shaped organs called lymph nodes. Clusters of lymph nodes are found in the underarm, pelvis, neck, and abdomen. The lymph nodes make and store infection-fighting cells. The spleen (an organ in the upper abdomen that makes lymphocytes and filters old blood cells from the blood), the thymus (a small organ beneath the breastbone), and the tonsils (an organ in the throat) are also part of the lymph system.

Because there is lymph tissue in many parts of the body, Hodgkin's disease can start in almost any part of the body. The cancer can spread to almost any organ or tissue in the body, including the liver, bone marrow (the spongy tissue inside the large bones of the body that makes blood cells), and spleen.

Lymphomas are divided into two general types: Hodgkin's disease and non-Hodgkin's lymphomas. The cancer cells in Hodgkin's disease look a certain way under a microscope. Non-Hodgkin's lymphomas are covered in the PDQ patient information summaries on non-Hodgkin's lymphoma (adult or childhood).

Source: NCI - Patient PDQ's on Hodgkins Disease