Lymphoma is a type of cancer that starts in cells of the lymph system, which is part of the body's immune system. There are 2 kinds of lymphomas:

• Hodgkin disease (named after Dr. Thomas Hodgkin, who recognized it in 1832)
• non-Hodgkin lymphoma

These 2 types of lymphomas behave, spread, and respond to treatment differently.

Non-Hodgkin lymphoma and Hodgkin disease occur about equally in children younger than 20 years old. Non-Hodgkin lymphoma usually occurs in younger children, while Hodgkin disease is more likely to affect older children and adolescents.

Hodgkin disease in children is very similar to Hodgkin disease in adults and is treated the same way. For more information on this disease, see the separate American Cancer Society document Hodgkin Disease.

The rest of this document focuses only on non-Hodgkin lymphoma in children.

The lymph system and lymphoid tissue

To understand non-Hodgkin lymphoma, it helps to know how the body's lymph system works.

The lymph system (also known as the lymphatic system) is composed mainly of lymphoid tissue, lymph vessels, and fluid called lymph (a clear fluid containing waste products and excess fluid from tissues). Lymphoid tissue is formed by several types of immune system cells that work together to help the body fight infections. Lymphoid tissue is found in many places throughout the body (described below).

Lymphocytes

Most of the cells found in lymphoid tissue are lymphocytes, a type of white blood cell. The 2 main types of lymphocytes are B lymphocytes (B cells) and T lymphocytes (T cells). Both types can become lymphoma cells, but B-cell lymphomas are much more common than T-cell lymphomas in the United States.

Normal B cells and T cells do different jobs within the immune system.

B cells help protect the body against germs (bacteria or viruses) by making proteins called antibodies. The antibodies attach to the bacteria or viruses, marking them for destruction by other parts of the immune system.

There are several types of T cells, each with a specialized job. Some T cells directly destroy certain kinds of bacteria or cells infected with viruses or fungi. Other types of T cells play a role in either boosting or slowing the activity of other immune system cells.

Lab tests identify B cells and T cells by certain substances on their surfaces. Some substances are found only on B cells, and others are found only on T cells. There are also several stages of B-cell and T-cell development (or maturation) that can be recognized by these lab tests.

Each type of lymphoma tends to resemble a particular subtype of normal lymphocytes at a certain stage of development. Because these types are treated differently, figuring out the type of lymphoma is the first step in determining treatment options.

Organs that contain 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 organs located throughout the body and connected by a system of lymphatic vessels. These vessels are like veins, except that instead of carrying blood, they carry lymph and immune system cells traveling between lymph nodes and other tissues.

Lymph nodes get bigger when they fight infection. Lymph nodes that grow in reaction to infection are called reactive nodes or hyperplastic nodes and are often painful to the touch. An enlarged lymph node in a child is not usually a sign of a serious problem. Enlarged lymph nodes in the neck are often felt 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 the section, "How is non-Hodgkin lymphoma in children diagnosed?"

Spleen: The spleen is an organ located under the lower part of the rib cage on the left side of the body. An average adult spleen weighs about 5 ounces, whereas the spleen of a 10-year-old is about 3 ounces. 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 gland: The thymus gland lies behind the upper part of the breastbone and in front of the heart. Before birth, the thymus plays a vital role in development of T lymphocytes. Although the thymus gland's size (about 1 ounce) and function decrease over the first 20 years of life, it continues to play a role in immune system function throughout life.

Adenoids and tonsils: These are collections of lymphoid tissue located at 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: The stomach and intestinal tract as well as many other organs also contain lymphoid tissue.

Bone marrow: The bone marrow (the soft inner part of 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 plug up small holes in blood vessels caused by cuts or scrapes. White blood cells' main job is fighting infections. The 2 main types of white blood cells are granulocytes and lymphocytes. Bone marrow lymphocytes are primarily B cells. Lymphomas sometimes start from bone marrow lymphocytes.

Types of non-Hodgkin lymphoma in children

Lymphomas are most often classified by how the cancer cells look under the microscope. Key features include the size and shape of the cells and how they are arranged (their pattern of growth).

• Size is described as large or small.
• Shape is described as cleaved (showing folds or indentations) or non-cleaved.
• The growth pattern may be either diffuse (cancer cells are scattered) or follicular (cells are arranged in clusters).

Not every lymphoma is described using all 3 features (size, shape, and pattern). Additional lab tests are often needed to accurately classify lymphomas. These are discussed in the section "How is non-Hodgkin lymphoma in children diagnosed?"

Nearly all non-Hodgkin lymphomas in children belong to 1 of 3 types:

• lymphoblastic lymphoma
• small non-cleaved cell (Burkitt) lymphoma
• large cell lymphoma

Although all 3 types are high grade (meaning they grow rapidly) and diffuse, it is important to distinguish among them because they are treated very differently.

Lymphoblastic lymphoma

Lymphoblastic lymphoma accounts for about 30% of lymphomas in children. It is most common in teenagers, and boys are affected twice as often as girls.

The cancerous cells of this lymphoma are lymphoblasts -- very young lymphocytes. They are the same cells as those seen in acute lymphoblastic leukemia (ALL) in children. If more than 25% of the bone marrow is involved, the disease is reclassified and treated as ALL.

Most cases of lymphoblastic lymphoma develop from T cells and are called precursor T-lymphoblastic lymphomas. These lymphomas often start in the thymus, forming a mass in the anterior mediastinum (the area behind the breast bone). This mass can cause problems with breathing. Trouble with breathing may be the first symptom of lymphoblastic lymphoma.

Less often, this cancer may develop in the tonsils, lymph nodes of the neck, or other lymph nodes. It can spread very quickly to the bone marrow, other lymph nodes, the surface of the brain, and/or the membranes that surround the lungs and heart.

A small fraction of lymphoblastic lymphomas develop from B-cells (precursor B-lymphoblastic lymphomas). These lymphomas more often begin in lymph nodes outside the chest, particularly in the neck. They can also involve the skin and bones.

Because lymphoblastic lymphoma can be a very rapidly growing disease and can interfere with breathing, it needs to be diagnosed and treated quickly.

Small non-cleaved non-Hodgkin lymphoma (Burkitt and non-Burkitt)

Small non-cleaved non-Hodgkin lymphoma accounts for about 40% to 50% of childhood non-Hodgkin lymphoma in the United States. It is most often seen in boys, usually around the age of 5 to 10 years old.

There are 2 types of small non-cleaved non-Hodgkin lymphoma: Burkitt type (also called Burkitt lymphoma after the doctor who first described this lymphoma in African children) and non-Burkitt type. However, children with either type are treated the same way.

In certain areas of Africa, the Burkitt-type small non-cleaved lymphoma accounts for nearly all childhood non-Hodgkin lymphoma and over half of all childhood cancers. For reasons that are not understood, in African children this lymphoma usually develops in the jaw or other facial bones.

Small non-cleaved lymphomas in other areas of the world, including the United States, almost always start in the abdomen. Typically, a child will develop a large tumor in his or her abdomen that can sometimes block the bowels (intestines). This can cause abdominal pain, nausea and vomiting. This lymphoma can also sometimes start in the neck or tonsils, or rarely in other parts of the body.

This lymphoma develops from B lymphocytes, and it is one of the most rapidly growing cancers known. It may spread to other organs, including the surface of the brain or inside the brain. Because of this, it must be diagnosed and treated quickly.

Large cell lymphomas

These lymphomas start in more mature forms of T cells or B cells almost anywhere in the body. They are not as likely to spread to the bone marrow or brain, nor do they grow as rapidly as other childhood lymphomas. There are 2 main subtypes of large cell lymphoma.

Anaplastic large cell lymphoma: This lymphoma represents about 10% of all non-Hodgkin lymphoma in children. It usually develops from mature T cells. It may start in lymph nodes in the neck or other areas, and may be found in the skin, lungs, bone, or other organs.

Diffuse large B-cell lymphoma: This lymphoma accounts for about 15% of childhood lymphomas. It starts in B cells, as the name implies. These lymphomas often become large masses in the mediastinum (the space between the lungs), but they are also sometimes found in lymphoid tissue in the neck or abdomen, or in the bones.

Treatment is the same for the different types of large cell lymphomas, but the cure rate tends to be slightly lower for the anaplastic type.

Last Medical Review: 07/08/2009
Last Revised: 07/08/2009