Other types of cancer -- lung or colon cancers, for example -- can spread to lymph tissue such as the lymph nodes or bone marrow. But cancers that start in these places and then spread to the lymph tissue are not lymphomas.

There are 2 main types of lymphomas. Hodgkin lymphoma (also known as Hodgkin's lymphoma, Hodgkin disease, or Hodgkin's disease) is named after Dr. Thomas Hodgkin, who first described it. Hodgkin disease is discussed in a separate American Cancer Society document. All other types of lymphoma are called non-Hodgkin lymphomas.

These 2 types of lymphoma can usually be distinguished from each other by looking at the cancer cells under a microscope. In some cases, sensitive lab tests may be needed to tell them apart.

The Lymph System and Lymphoid Tissue

To understand what lymphoma is, it helps to know about the body's lymph system.

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 develop into lymphoma cells, but B-cell lymphomas are much more common than T-cell lymphomas in the United States.

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

B cells normally help protect the body against germs (bacteria or viruses) by making proteins called antibodies. The antibodies attach to the bacteria or viruses and attract other immune system cells that surround and digest the antibody-coated germs. Antibodies also attract certain blood proteins that can kill bacteria.

There are several types of T cells, each with a specialized job. Some normal T cells help protect the body against viruses, fungi, and some bacteria. They recognize specific substances found in virus-infected cells and destroy these cells. T cells can also release substances called cytokines that attract certain other types of white blood cells, which then digest the infected cells. T cells are also thought to destroy some types of cancer cells, as well as the cells of transplanted organs. Some 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.

This information is helpful because each type of lymphoma tends to resemble a particular subtype of normal lymphocytes at a certain level of development. Determining the type of lymphoma a person has is the first step in considering 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 tender to the touch. An enlarged lymph node is not usually a sign of a serious problem. Enlarged lymph nodes in the neck are often felt in people 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 Diagnosed?"

Spleen: The spleen is located under the lower part of the rib cage on the left side of the body. An average adult spleen weighs about 5 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. The thymus gland's size (about 1 ounce) and function diminish over the first 20 years of life. Despite this, the thymus continues to be active 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 or if they become cancerous.

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

Classifying non-Hodgkin lymphoma can be quite confusing (even for many doctors) because there are so many types (around 30) and because several different systems have been used. The most recent system is the World Health Organization (WHO) classification. The WHO system uses the appearance of the lymphoma cells, the chromosome features of the cells, and the presence of certain chemicals on the surface of the cells. (Older systems classified lymphomas based only on their appearance under a microscope.)

This overview classifies the most common lymphomas according to whether they are B-cell or T-cell lymphomas and lists them by how common they are. Some rarer forms of non-Hodgkin lymphoma are not discussed here.

B-Cell Lymphomas

B-cell lymphomas make up most (about 85%) of non-Hodgkin lymphomas in the United States.

Diffuse Large B-cell Lymphoma

This is one of the more common types of non-Hodgkin lymphoma in the United States, accounting for about 1 out of every 3 cases. The cells are fairly large when viewed under the microscope.

Diffuse large B-cell lymphoma DLBCL can affect any age group but occurs mostly in older people (the average age of most patients is mid-60s). The usual symptoms are a quickly growing mass in an internal lymph node, such as in the chest or abdomen or in a lymph node that you can feel, for example, in the neck or armpit. Although this lymphoma usually starts in lymph nodes, it can grow in other areas such as the intestines, bone, and even the brain or spinal cord.

About 1 out of 3 of these lymphomas is confined to one part of the body (localized). When it is localized, this type of lymphoma is considered to be more curable than when it has spread to other parts of the body. Genetic tests have shown that there are different subtypes of DLBCL, even though they look the same under the microscope. These subtypes seem to have different outlooks (prognoses) and responses to treatment.

This is a fast growing lymphoma, but it often responds well to treatment with chemotherapy. Overall, about 3 out of 4 people will have no signs of disease after initial treatment, and about half of all people with this lymphoma are cured with therapy.

Follicular Lymphoma

About 1 out of 4 lymphomas in the United States are follicular lymphomas. The term follicular is used because the cells tend to grow in a circular, or nodular, pattern in lymph nodes.

The average age for people with this lymphoma is about 60. It is rare in very young people. Most of the time, this lymphoma occurs in many lymph node sites in the body, as well as in the bone marrow. In about 10% of cases, it only involves lymph nodes in one part of the body.

Although it is usually not considered curable by standard treatment, this is often a very slow-growing lymphoma, and the 5-year survival rate (the percentage of people surviving at least 5 years) is around 60% to 70%. Often these lymphomas are not treated when they are first diagnosed if the patient has no symptoms of the disease. Over time, out of 3 follicular lymphomas about 1 changes (transforms) into a fast-growing diffuse B-cell lymphoma.

Chronic Lymphocytic Leukemia /Small Lymphocytic Lymphoma

These related diseases account for about 1 out of 4 lymphomas. The same type of cell (known as a small lymphocyte) is involved in both chronic lymphocytic leukemia (CLL) and small lymphocytic leukemia (SLL). The only difference is where the cancer occurs. In CLL it is mostly in the blood and bone marrow; in SLL, it is mainly in the lymph nodes.

Both are slow-growing diseases, although CLL, which is much more common, tends to grow slower. CLL and SLL are not considered curable with standard treatments, but depending on the stage and growth rate of the disease, most patients can live longer than 10 years. Occasionally over time, these slow-growing lymphomas transform into a more aggressive type of lymphoma.

For more detailed information, see the American Cancer Society document, Leukemia -- Chronic Lymphocytic.

Mantle Cell Lymphoma

Only about 5% of lymphomas are of this type. The cells are small to medium.

Men are affected most often. The average age of patients is in the early 60s. The lymphoma is usually widespread when it is diagnosed, involving lymph nodes, bone marrow, and, very often, the spleen.

Although this isn't a very fast growing lymphoma, it is hard to treat. Only about 1 in 5 patients survive at least 5 years. Newer, more aggressive treatments may be more effective than those used in the past, which may help improve the survival rates of patients now being diagnosed.

Marginal Zone B-cell Lymphomas

Marginal zone lymphomas account for about 4% of lymphomas. The cells in these lymphomas look small under the microscope. There are 3 main types of marginal zone lymphomas.

Extranodal marginal zone B-cell lymphomas (also known as mucosa-associated lymphoid tissue lymphomas): These lymphomas start in places other than the lymph nodes (hence the name "extranodal")and are the most common type. Most mucosa-associated lymphoid tissue (MALT) lymphomas arise in the stomach and are thought to be related to an infection by the bacteria Helicobacter pylori, which is also the cause of stomach ulcers. Other possible sites of MALT lymphomas include the lung, skin, thyroid, salivary glands, and tissues surrounding the eye. Usually it is confined to the area where it begins and is not widespread. Many of these other MALT lymphomas have also been linked to infections with bacteria or viruses.

The average age of patients with this lymphoma is about 60. It is a slow-growing lymphoma and is often curable in its early stages. Doctors often use antibiotics as the first treatment for this type of lymphoma, especially MALT lymphoma of the stomach, as they may get rid of the Helicobacter pylori infection.

Nodal marginal zone B-cell lymphoma: This is a rare disease, found mainly in older women. Mostly lymph nodes are involved, although the cells can also sometimes be found in the bone marrow.

This tends to be a slow-growing lymphoma (although not usually as slow as MALT lymphoma), and many patients are cured if they are diagnosed in the early stages.

Splenic marginal zone B-cell lymphoma: This is a rare lymphoma. Most often the lymphoma is found only in the spleen and bone marrow.

Patients are often elderly and male and suffer from fatigue and discomfort caused by an enlarged spleen. Because the disease is slow-growing, treatment may not be needed unless the symptoms become troublesome.

Primary Mediastinal B-cell Lymphoma

This type accounts for about 2% of all lymphomas. The cells are large and resemble those of diffuse large B-cell lymphomas.

This lymphoma starts in the mediastinum (the area around the heart and behind the chest bone). It usually is localized at the beginning and rarely involves the bone marrow. It can cause trouble breathing because it often presses on the windpipe (trachea) leading into the lungs. It can also block the superior vena cava (the large vein that returns blood to the heart from the arms and head). This can cause the arms and face to swell.

About 2 out of 3 people with this lymphoma are women. Most are young -- in their 30s. It is a fast growing lymphoma but it is treatable. About half of patients can be cured.

Burkitt Lymphoma

This type makes up about 1% to 2% of all lymphomas. It is named after the doctor who first described this disease in African children and young adults. The cells are medium sized. Another kind of lymphoma, called Burkitt-like lymphoma, has slightly larger cells. Because this second kind of lymphoma is hard to tell apart from Burkitt lymphoma, the WHO classification combines them.

This is a very fast-growing lymphoma. In the African variety, it often starts as tumors of the jaws or other facial bones. In the more common types seen in the United States, the lymphoma usually starts in the abdomen, where it forms a large tumor mass. It can also start in the ovaries, testes, or other organs, and can spread to the brain and spinal fluid.

Close to 90% of patients are male, and the average age is about 30. Although this is a fast-growing lymphoma, over half of patients can be cured by intensive chemotherapy.

Lymphoplasmacytic Lymphoma (Waldenstrom Macroglobulinemia)

This type is not common, accounting for 1% to 2% of lymphomas. The cells are small and found mainly in the bone marrow, lymph nodes, and spleen.

Most of the time the lymphoma cells make an antibody called immunoglobulin M (IgM), which is a very large protein. This antibody circulates in the blood in large amounts, and causes the liquid part of the blood to thicken, like syrup. This can lead to decreased blood flow to many organs, which can cause problems with vision (because of poor circulation in blood vessels in the back of the eyes) and neurological problems (such as headache, dizziness, and confusion) caused by poor blood flow within the brain. Other symptoms can include feeling tired and weak, and a tendency to bleed easily.

This lymphoma is slow growing. Although it isn't usually considered to be curable, most patients live longer than 5 years.

For more information, see the American Cancer Society document, Waldenstrom Macroglobulinemia.

Hairy Cell Leukemia

Despite the name, this is sometimes considered to be a type of lymphoma. This disease is rare -- about 1,000 people in the United States are diagnosed with this type each year. The cells are small B lymphocytes with projections around them that give them a "hairy" appearance. They are typically found in the bone marrow and spleen and circulating in the blood.

Patients tend to be older in general. Hairy cell leukemia is slow-growing, and some patients may never need treatment. An enlarging spleen or dropping blood counts (due to cancer cells invading the bone marrow) are the usual reasons to begin treatment, which is highly effective. Hairy cell leukemia is also described in the separate American Cancer Society document, Leukemia--Chronic Lymphocytic.

Primary Central Nervous System Lymphoma

This lymphoma usually involves the brain (called primary brain lymphoma), but it may also be found in the spinal cord and in tissues around the spinal cord and the eye. Over time, it tends to become widespread in the central nervous system. Although this was a rare tumor in the past, it has become more common in patients with acquired immune deficiency syndrome (AIDS). Most people develop headache and confusion. They can also have vision problems, paralysis of some facial muscles, and even seizures in some cases.

The outlook for people with this condition has always been thought to be fairly poor, but about 30% to 50% of people can live at least 5 years with today's treatments.

T-Cell Lymphomas

T-cell lymphomas represent less than 15% of non-Hodgkin lymphomas in the United States.

Precursor T-lymphoblastic Lymphoma/Leukemia

This disease accounts for about 1% of all lymphomas. It can be considered either a lymphoma or leukemia, depending on how much of the bone marrow is involved (leukemias have more bone marrow involvement). The cancer cells are small-to-medium immature T-cells.

It often starts in the thymus gland (where many T cells are made) and can develop into a large tumor in the mediastinum (the area around the heart and behind the breast bone). This can cause trouble breathing if it presses on the windpipe (trachea) leading into the lungs. It can also block the superior vena cava (the large vein that returns blood to the heart from the arms and head), which can cause the arms and face to swell.

Patients are most often young adults, with males being affected more often than females.

This lymphoma is fast-growing, but if it hasn't spread to the bone marrow when it is first diagnosed, the chance of cure with chemotherapy is quite good. Once it is in the bone marrow, only about 40% to 50% of patients can be cured.

Peripheral T-cell Lymphomas

These lymphomas develop from more mature forms of T cells. There are several kinds of peripheral T-cell lymphomas, which in total account for about 5% of all lymphomas.

• Cutaneous T-cell lymphomas (mycosis fungoides, Sezary syndrome): These T-cell lymphomas start in the skin. They are described in the American Cancer Society document, Lymphoma of the Skin. 
• Angioimmunoblastic T-cell lymphoma: This lymphoma tends to occur in the lymph nodes and may affect the spleen or liver. Patients usually have fever, weight loss, and skin rashes and often develop infections. This lymphoma often progresses quickly, although some patients get better with cortisone-like drugs (corticosteroids) such as prednisone and/or chemotherapy. But it's not clear that this lymphoma can be cured, and intensive chemotherapy with a stem cell transplant is often used. 
• Extranodal natural killer/T-cell lymphoma, nasal type: This type often involves the upper airway passages, such as the nose and upper throat, but it can also invade the skin and digestive tract. It is much more common in parts of Asia and South America. All ages can be affected. If the lymphoma is localized to the nasal passages, it can often be cured by chemotherapy and radiotherapy. But if it is widespread, then only a few patients are cured by very aggressive chemotherapy. 
• Enteropathy type T-cell lymphoma: This lymphoma occurs in people with sensitivity to gluten, the main protein in wheat flour. The disease, called gluten-sensitive enteropathy, can progress to this lymphoma, which typically invades the walls of the intestines. Once it occurs, the patient's outlook is usually poor because of damage to the intestines. 
• Subcutaneous panniculitis-like T-cell lymphoma: This rare lymphoma invades the deep layers of the skin, where it causes nodules to form. It is described further in the American Cancer Society document, Lymphoma of the Skin.  
• Anaplastic large cell lymphoma: About 1% to 2% of lymphomas are of this type. The cells appear large under the microscope. The type of lymphoma is more common in young people, but it does occur in patients in their 50s and 60s. It usually starts in lymph nodes and can also spread to skin. There is also a form that begins in the skin. Although this type of lymphoma appears to be fast-growing, chemotherapy often works well. Many patients with this lymphoma are cured. 
• Peripheral T-cell lymphoma, unspecified: This name is given to T-cell lymphomas that don't readily fit into any of the groups above. The tumor cells can be small or large. Most patients are in their 60s. As a group, these lymphomas tend to be widespread and grow quickly. Some cases respond well to chemotherapy, although few patients survive beyond 5 years.