Although CD is not officially a cancer, the "multicentric" form of this disease acts very much like lymphoma (cancer of lymph nodes). In fact, many people with this disease eventually develop lymphomas. This is why it is included in the American Cancer Society’s cancer information database. (For information about lymphoma, see the American Cancer Society documents, Hodgkin Disease and Non-Hodgkin Lymphoma.) Instead of being called a cancer, CD is often called a lymphoproliferative disorder -- meaning there is an abnormal overgrowth of lymph nodes -- similar in many ways to lymphomas. Like lymphoma, CD is frequently treated with chemotherapy or radiation therapy.

About lymph nodes and lymphoid tissue

Lymphoid tissue, also known as lymphatic tissue, is the main part of the immune system. It is formed by different types of cells that work together to resist infections. Lymphoid tissue also has a role in the body's resistance against some forms of cancer. The main cell of lymphoid tissue is the lymphocyte. There are 2 types of lymphocytes: B cells and T cells.

Lymphoid tissue is found in many places throughout the body, including:

• lymph nodes (bean-sized collections of immune system cells found clustered in the groin and underarm areas, on the sides of the neck, inside the chest, and scattered widely though the body including the abdomen) 
• thymus gland (found behind the chest bone and in front of the heart) 
• spleen (on the left side of the abdomen next to the stomach) 
• tonsils and adenoids 
• bone marrow

Types of Castleman disease

The 2 main forms of Castleman disease are localized and multicentric. They affect people very differently.

Localized Castleman disease

Localized or unicentric Castleman disease (CD) only affects a single lymph node and is not widespread. The lymph nodes in the chest and abdomen are affected most often. CD causes these lymph nodes to enlarge. These abnormally large lymph nodes may press on other organs and tissues inside the chest or abdomen. If they are in the abdomen, the person might feel abdominal discomfort. Enlarged lymph nodes in the chest can press on the windpipe (trachea) or smaller breathing tubes (bronchi) causing breathing problems. Sometimes the enlarged lymph nodes are in places such as the neck, groin, or underarms and can be felt easily. People with localized CD disease are usually cured when the lymph node is surgically removed..

Multicentric Castleman disease

Multicentric Castleman disease (CD) affects more than one group of lymph nodes and may also affect other organs containing lymphoid tissue. This form sometimes occurs in people infected with human immunodeficiency virus (HIV), the virus that causes AIDS. Multicentric CD is more serious than the localized type, particularly in people with HIV infection.

People with multicentric CD often have serious infections, fevers, weight loss, fatigue, night sweats, and nerve damage that can cause weakness and numbness. Blood tests often show too few red blood cells (anemia) and high levels of antibodies in the blood (hypergammaglobulinemia). CD can weaken the immune system severely, making it hard to fight infection. Infections in people with multicentric CD can be very serious - even causing death. CD also increases the risk of developing malignant lymphomas, which may be fatal.

Microscopic subtypes of Castleman disease

Castleman disease can also be classified as either a hyaline vascular type or a plasma cell type based on how the lymph node tissue appears under a microscope. Less often, a combination of both types may occur. The hyaline vascular type is more common and tends to be localized, while the plasma cell type tends to be multicentric, but exceptions to this rule often occur. In choosing treatments, doctors consider the microscopic type less important than whether the disease is localized or multicentric.