Cancer starts when cells in the body begin to grow out of control. Cells in nearly any part of the body can become cancer, and can spread to other areas of the body. To learn more about how cancers start and spread, see What Is Cancer?
Lymphoma is a type of cancer that starts in cells called lymphocytes, which are part of the body’s immune system. There are 2 kinds of lymphomas:
- Hodgkin disease (also known as Hodgkin lymphoma), which is named after Dr. Thomas Hodgkin, who first described it
- Non-Hodgkin lymphoma (NHL)
These types of lymphomas behave, spread, and respond to treatment differently, so it is important to tell them apart.
Both types of lymphoma are more common in adults, but they can also occur in children and teens. Among this younger age group, NHL tends to occur in younger children, while Hodgkin disease is more likely to affect older children and teens.
Hodgkin disease is very similar in adults and children, and treatment is the same for both. For more information on this disease, see our document Hodgkin Disease.
The rest of this document is only about non-Hodgkin lymphoma in children.
The lymph system and lymphoid tissue
To understand NHL, it helps to know about the body’s lymph system.
The lymph system (also known as the lymphatic system) is part of the body’s immune system, which helps fight infections and some other diseases. It also helps fluids move around within the body. The lymph system is made up mainly of:
- Lymphoid tissue: includes the lymph nodes and related organs (see below) that are part of the body’s immune and blood-forming systems
- Lymph: a clear fluid that travels through the lymph system, carrying waste products and excess fluid from tissues, as well as lymphocytes and other immune system cells
- Lymphatic vessels: small tubes, similar to blood vessels, through which lymph travels to different parts of the lymph system
Lymphoid tissue is made up mainly of cells called lymphocytes, a type of white blood cell. The 2 main types of lymphocytes are B lymphocytes (B cells) and T lymphocytes (T cells). Normal B cells and T cells do different jobs.
B lymphocytes: B cells normally help protect the body against germs (bacteria or viruses) by making proteins called antibodies. The antibodies attach to the germs, marking them for destruction by other parts of the immune system.
T lymphocytes: There are several types of T cells, each with a special job. Some T cells directly destroy cells infected with viruses, fungi, or certain kinds of bacteria. Other types of T cells play a role in either boosting or slowing the activity of other immune system cells.
Both types of lymphocytes can develop into lymphoma cells, but B-cell lymphomas are much more common in the United States than T-cell lymphomas. Different types of lymphoma can develop from both B and T lymphocytes, based on how mature the cells are when they become cancerous and other factors.
Treatment for lymphoma depends on which type it is, so determining the exact type of lymphoma is important.
Organs that have lymphoid tissue
Because lymphoid tissue is in many parts of the body, lymphomas can start almost anywhere.
The major sites of lymphoid tissue are:
Lymph nodes: Lymph nodes are bean-sized collections of lymphocytes and other immune cells throughout the body. They can sometimes be felt under the skin in the neck, under the arms, and in the groin. Lymph nodes are connected to each other by a system of lymphatic vessels.
Lymph nodes get bigger when they fight infection. Lymph nodes that grow because of infection are called reactive nodes or hyperplastic nodes and are often painful when they are touched. An enlarged lymph node in a child is not usually a sign of a serious problem. Lymph nodes in the neck are often enlarged in children with sore throats or colds. But a large lymph node is also the most common sign of lymphoma. Lymph node enlargement is discussed more in “Signs and symptoms of non-Hodgkin lymphoma in children.”
Spleen: The spleen is an organ under the lower part of the rib cage on the left side of the body. The spleen makes lymphocytes and other immune system cells to help fight infection. It also stores healthy blood cells and filters out damaged blood cells, bacteria, and cell waste.
Thymus: The thymus is a small organ behind the upper part of the breast bone and in front of the heart. Before birth, the thymus plays a vital role in development of T lymphocytes. The thymus shrinks and becomes less important as people get older, but it continues to play a role in immune system function.
Adenoids and tonsils: These are collections of lymphoid tissue in the back of the throat. They help make antibodies against germs that are breathed in or swallowed. They are easy to see when they become enlarged during an infection, which occurs often in children, or if a lymphoma develops.
Digestive tract: Lymphoid tissue is also in the stomach and intestines, as well as many other organs.
Bone marrow: The bone marrow (the soft inner part of certain bones) makes red blood cells, blood platelets, and white blood cells. Red blood cells carry oxygen from the lungs to the rest of the body. Platelets help control bleeding by plugging up small holes in blood vessels. White blood cells fight infections. The main types of white blood cells are granulocytes and lymphocytes. Bone marrow lymphocytes are mainly B cells. Lymphomas sometimes start from bone marrow lymphocytes.
Last Revised: 01/27/2016