Introduction:

Hodgkin's disease is a type of lymphoma. Lymphomas are cancers of the lymphatic system. They are generally subdivided into two groups: Hodgkin's disease (HD) and non-Hodgkin's lymphoma (NHL). NHL is discussed in another report. [For more information, see In-Depth Report #84: Non-Hodgkin's lymphomas.] Hodgkin� ' s disease is also called Hodgkin� ' s lymphoma.

The lymphatic system filters fluid from around cells. It is an important part of the immune system. When people talk about swollen glands in the neck, they are usually referring to swollen lymph nodes. Common areas where lymph nodes can be easily felt, especially if enlarged, are: the groin, armpits (axilla), above the clavicle (supraclavicular), in the neck (cervical), and the back of the head just above hairline (occipital).

Hodgkin� ' s disease is marked by the presence of abnormal large cells called Reed-Sternberg cells. Reed-Sternberg cells are derived from B cell lymphocytes (white blood cells). Reed-Sternberg cells are specific to Hodgkin� ' s disease. They are not found in non-Hodgkin� ' s lymphoma.

Most often HD starts in B cell lymphocytes located in lymph nodes in the neck area, although any lymph node may be the site of initial disease.

Types of Hodgkin's Disease

There are two major types of Hodgkin� ' s disease: Classical Hodgkin� ' s lymphoma and nodular lymphocyte-predominant Hodgkin� ' s disease.

Classical Hodgkin's Lymphoma. Classical Hodgkin� ' s lymphoma accounts for about 95% of Hodgkin� ' s disease cases. It has four major subtypes:

• Nodular Sclerosis. Nodular sclerosis is the most common subtype, representing about 60 - 80% of HD cases. Younger patients are more likely to have this type. The nodes first affected are often those located in the center of the chest (the mediastinum) or the neck.
• Mixed Cellularity. Mixed cellularity is the next most common HD form, occurring in about 15 - 30% of patients, mostly in older adults. Mixed cellularity refers to the presence of Reed-Sternberg cells and other cell types.
• Lymphocyte Rich. The lymphocyte-rich subtype accounts for about 5% of all HD cases. It tends to affect men more than women.
• Lymphocyte Depleted. The lymphocyte-depleted subtype is the least common type of HD, occurring in only about 1% of cases. It is usually seen in older people and patients infected with HIV. It is also more common in less developed countries. The cancer tends to be diagnosed when it is widespread, affecting the spleen, bone marrow, and liver as well as abdominal lymph nodes.

Nodular Lymphocyte-Predominant Hodgkin's Disease. Nodular lymphocyte-predominant Hodgkin's disease occurs in about 5% of patients. It is distinct from classical Hodgkin� ' s lymphoma. The cells look like and are referred to as “popcorn” cells, which are variants of Reed-Sternberg cells. This type of HD typically affects younger patients and usually originates in the neck lymph nodesThis type of HD is sometimes confused with non-Hodgkin� ' s lymphoma (NHL). In fact, there is a 3 - 5% risk that nodular lymphocyte-predominant Hodgkin� ' s disease can transform into diffuse large B-cell NHL.

The Lymphatic System

Lymphomas represent tumors of the lymphatic system. This system is a network of organs, ducts, and nodes. The system interacts with the blood's circulatory system to transport a watery clear fluid called lymph throughout the body. The lymphatic system contains lymphocytes, which are important cells involved in defending the body against infections. This system also restores 60% of the fluid that leaks out from blood capillaries back into circulation. Its ducts provide transportation for fats, proteins, and other substances collected from the body's tissues.

Lymphocytes. The lymphatic system helps produce and transport lymphocytes, white blood cells that are a primary component of the immune system. Some lymphocytes produce antibodies that can target and attack specific foreign substances (antigens).

• Lymphocytes develop in the bone marrow or thymus gland. They are categorized as either B cells (bone marrow-derived cells) or T cells (thymus gland-derived cells).
• Lymphatic vessels begin as tiny tubes. They lead to larger lymphatic ducts and branches, and drain into two ducts in the neck, where the fluid re-enters the bloodstream.
• Along the way, the fluid passes through lymph nodes, which are oval structures composed of lymph vessels, connective tissue, and white blood cells. Here, the lymphocytes are either filtered out or added to the contents of the node.
• Both leukemia and lymphomas (Hodgkin� ' s disease and non-Hodgkin� ' s lymphomas) are cancers of lymphocytes. The difference is that leukemia starts in the bone marrow while lymphomas originate in lymph nodes and then spread to the bone marrow or other organs.

Lymph Nodes. In a lymph node, lymphocytes typically receive their initial exposure to foreign substances, such as bacteria. This exposure prompts the lymphocytes to perform their immune functions. The size of a lymph node varies generally from that of a pinhead to a bean. Most nodes are clustered throughout the body. Important node clusters are found in the neck, lower arm, armpit, and groin.

Other Structures in the Lymphatic System. The tonsils and adenoids are secondary lymphatic organs. They are composed of masses of lymph tissue that also play a role in the lymphatic system. The spleen is another important organ that processes lymphocytes from incoming blood.

Spread of Cancer. Hodgkin's disease usually progresses in an orderly way from one lymph node region to the next. This process may be slow, particularly in younger people, or very aggressive. The disease typically spreads downward from the initial site.

• If it spreads below the diaphragm, it usually reaches the spleen first; the disease may then spread to the liver and bone marrow.
• If the disease starts in the nodes in the middle of the chest, it may spread outward to the chest wall and areas around the heart and lungs.