Childhood Hodgkin lymphoma is a disease in which malignant (cancer) cells form in the lymph system.

Childhood Hodgkin lymphoma is a type of cancer that develops in the lymph system, part of the body's immune system. The lymph system is made up of the following:

• Lymph: Colorless, watery fluid that travels through the lymph system and carries white blood cells called lymphocytes. Lymphocytes protect the body against infections and the growth of tumors.
• Lymph vessels: A network of thin tubes that collect lymph from different parts of the body and return it to the bloodstream.
• Lymph nodes: Small, bean-shaped structures that filter lymph and store white blood cells that help fight infection and disease. Lymph nodes are located along the network of lymph vessels found throughout the body. Clusters of lymph nodes are found in the underarm, pelvis, neck, abdomen, and groin.
• Spleen: An organ that makes lymphocytes, filters the blood, stores blood cells, and destroys old blood cells. The spleen is on the left side of the abdomen near the stomach.
• Thymus: An organ in which lymphocytes grow and multiply. The thymus is in the chest behind the breastbone.
• Tonsils: Two small masses of lymph tissue at the back of the throat. The tonsils make lymphocytes.
• Bone marrow: The soft, spongy tissue in the center of large bones. Bone marrow makes white blood cells, red blood cells, and platelets.

Anatomy of the lymph system, showing the lymph vessels and lymph organs including lymph nodes, tonsils, thymus, spleen, and bone marrow. Lymph (clear fluid) and lymphocytes travel through the lymph vessels and into the lymph nodes where the lymphocytes destroy harmful substances. The lymph enters the blood through a large vein near the heart.

Because lymph tissue is found throughout the body, Hodgkin lymphoma can start in almost any part of the body and spread to almost any tissue or organ in the body.

Lymphomas are divided into two general types: Hodgkin lymphoma and non-Hodgkin lymphoma. (See the PDQ summary on Childhood Non-Hodgkin Lymphoma Treatment for more information.)

Hodgkin lymphoma can occur in both children and adults; however, treatment for children may be different than treatment for adults. (See the PDQ summary on Adult Hodgkin Lymphoma Treatment for more information.)

There are two types of childhood Hodgkin lymphoma.

The two types of childhood Hodgkin lymphoma are:

• Classical Hodgkin lymphoma.
• Nodular lymphocyte-predominant Hodgkin lymphoma.

Classical Hodgkin lymphoma is divided into four subtypes, based on how the cancer cells look under a microscope:

• Lymphocyte-rich classical Hodgkin lymphoma.
• Nodular sclerosis Hodgkin lymphoma.
• Mixed cellularity Hodgkin lymphoma.
• Lymphocyte-depleted Hodgkin lymphoma.

Age, gender, and Epstein-Barr virus infection can affect the risk of developing childhood Hodgkin lymphoma.

Anything that increases your risk of getting a disease is called a risk factor. Having a risk factor does not mean that you will get cancer; not having risk factors doesn’t mean that you will not get cancer. People who think they may be at risk should discuss this with their doctor. Risk factors for childhood Hodgkin lymphoma include the following:

• Being between the ages of 5 and 14. In children younger than 14 years, it is more common in boys than in girls.
• Being infected with the Epstein-Barr virus.
• Having a brother or sister with Hodgkin lymphoma.