Lymphoma is a cancer that starts in cells called lymphocytes, which are part of the body's immune system. Lymphocytes are in the lymph nodes and other lymphoid tissues (such as the spleen, bone marrow, and some other organs, including the skin).
Some other types of cancer – lung or colon cancers, for example – can spread to lymph tissue such as the lymph nodes. But cancers that start in these places and then spread to the lymph tissue are not lymphomas. Lymphomas, by definition, start in lymphocytes in either the lymph nodes or other lymphoid tissue.
When a lymphoma starts only in the skin (not other organs or tissues) it is called a skin lymphoma (or cutaneous lymphoma). A lymphoma that starts in lymph nodes or another part of the body and then spreads to the skin is not considered a skin lymphoma (because it didn't start there).
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.
- Non-Hodgkin lymphoma (also known as non-Hodgkin's lymphoma, NHL, or sometimes just lymphoma) includes all other lymphomas. All skin lymphomas are non-Hodgkin lymphomas.
These 2 main types of lymphomas differ in how they behave, spread, and respond to treatment. Doctors can usually tell the difference between them by looking at the cancer cells under a microscope. In some cases, sensitive lab tests may be needed to tell them apart.
Hodgkin disease and other types of non-Hodgkin lymphoma are discussed in separate American Cancer Society documents. The rest of this document focuses only on lymphoma of the skin.
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 a clear fluid called lymph. Lymphoid tissue is found in many places throughout the body. It is made up of several types of immune system cells that work together to help the body fight infections.
Lymphocytes
Most of the cells 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). Normal B cells and T cells do different jobs within the immune system.
B lymphocytes: 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 then surround and digest the antibody-coated germs. Antibodies also attract certain blood proteins that can kill bacteria.
T lymphocytes: There are several types of T cells, each with a specialized job. Some T cells help protect the body against viruses, fungi, and some bacteria. For example, 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. Some 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. Overall, B-cell lymphomas are much more common than T-cell lymphomas in the United States. In the skin, though, T-cell lymphomas are more common than B-cell lymphomas. Several different types of lymphoma can develop from each type of lymphocyte.
B-cells and T-cells can be recognized by lab tests that detect certain proteins on their surfaces and certain features of their DNA. There are also several stages of B-cell and T-cell development that can be recognized by these lab tests.
This information is important because each type of lymphoma tends to resemble a particular subtype of normal lymphocytes at a certain stage of development. Determining the type of lymphoma a person has is the first step in considering treatment options.
Lymphoid tissue
Most lymphocytes are found in lymph nodes, which are small, bean-sized collections of immune cells found throughout the body. Lymph nodes make and store lymphocytes, and are the major tissue in the lymphatic system. Lymph nodes are connected throughout the body by narrow tubes similar to blood vessels called lymphatics (or lymph vessels). Lymph vessels carry a colorless, watery fluid (lymph) that contains lymphocytes. Eventually this fluid empties into the bloodstream.
Along with the lymph nodes, collections of lymphocytes can be found in many other places in the body, including the:
- Spleen
- Bone marrow
- Thymus
- Adenoids and tonsils
- Digestive tract
- Skin
- Other organs
Lymphomas can start in any part of the body that contains lymphoid tissue.
Types of lymphoma of the skin
Classifying lymphoma of the skin can be quite confusing (even for many doctors) because there are many types and they are not that common.
The newest system of classification was put together by doctors from the World Health Organization (WHO) and the European Organization for Research and Treatment of Cancer (EORTC) and is called the WHO-EORTC classification. It classifies the lymphomas based on 2 important pieces of information:
- How they look under the microscope
- Whether there are certain proteins on the lymphoma cells (based on lab tests)
Using this combined information, the various types of skin lymphoma can be identified.
T-cell skin lymphomas
Mycosis fungoides: This type accounts for about half of all skin lymphomas. Mycosis fungoides (MF) can occur at any age, but most patients are in their 50s and 60s. Men are almost twice as likely as women to develop this lymphoma.
The first sign of this disease is one or more patchy, scaly, red lesions on the skin. MF lesions can be very itchy. Often these lesions are the only symptom of MF. But in some people the disease can progress to more solid, raised tumors on the skin that can become bigger. Because it can be confused with other skin problems, MF may be hard to diagnose at first. Often, multiple biopsy samples of the lesions are taken before the diagnosis is confirmed.
In time, the lymphoma can spread across the skin or invade lymph nodes and organs like the liver. In many patients this disease grows slowly, but it can be faster growing in older patients. Some people with MF go on to develop Sezary syndrome.
Sezary syndrome: This disease is often looked upon as an advanced form of mycosis fungoides, but these are actually 2 different diseases. In Sezary syndrome (SS) the skin is involved all over instead of in patches. The rash is widespread, very itchy, and red, and can look like a sunburn. This is called generalized erythroderma. The skin is often thickened. Lymphoma cells, called Sezary cells, can also be found in the bloodstream. These cells are found in the lymph nodes as well.
Patients with SS often have weakened immune systems, which increases their risk of serious infections. Whereas MF is usually slow growing, SS is more aggressive and tends to grow and spread faster.
Primary cutaneous anaplastic large cell lymphoma: This lymphoma usually starts as a single tumor on the skin. Sometimes, though, several tumors may develop. The tumors can vary in size, with some as small as a pimple and others the size of a quarter, or even larger.
Most people with this disease are in their 50s and 60s, but it can also occur in children. It is found at least twice as often in men as in women. In most cases it does not spread beyond the skin, and the prognosis (outlook) is very good.
Lymphomatoid papulosis: This disorder of the skin is seen in younger people more often than the other T-cell skin lymphomas, with an average age of around 45. Men get this disease more often than women. This is a benign, slow-growing disease that often comes and goes on its own, even without treatment.
Under the microscope, lymphomatoid papulosis has certain features that may look like primary cutaneous anaplastic large cell lymphoma. It often begins as several large pimple-like lesions that may develop an ulcer in the middle.
This disease often goes away without treatment, but it can take anywhere from a few months to many years to go away completely. Lymphomatoid papulosis doesn't spread to internal organs and is not fatal. Rarely, some people with this skin disorder develop some other type of lymphoma that is more serious.
Subcutaneous panniculitis-like T-cell lymphoma: This rare lymphoma invades the deepest layers of the skin, where it causes nodules to form. Most often these develop on the legs, but they can occur anywhere on the body. This lymphoma affects all ages and both sexes equally. It usually grows slowly and tends to have a good prognosis.
Primary cutaneous peripheral T-cell lymphoma, unspecified: This is a group of rare skin lymphomas that don't fit into any special category. There are several types.
- Primary cutaneous aggressive epidermotropic CD8+ cytotoxic T-cell lymphoma develops as widespread patches, nodules and tumors. It can sometimes look like mycosis fungoides, but the biopsy will show that it is this specific tumor.
- Cutaneous gamma/delta T-cell lymphoma develops as thickened skin plaques or actual tumors, mainly on the arms and legs, but sometimes in the intestines or lining of the nose. This is a very aggressive lymphoma that spreads quickly. In older classification systems, this was considered a subtype of subcutaneous panniculitis-like T cell lymphoma.
- Primary cutaneous CD4+ small/medium sized pleomorphic T-cell lymphoma often starts as a single area of thickening of the skin or a tumor, but later there may be multiple tumors.
- Skin lymphomas that don't fall into any of these 3 categories are called simply primary cutaneous peripheral T-cell lymphoma, unspecified. People can have either single or multiple nodules.
B-cell skin lymphomas
Primary cutaneous marginal-zone B-cell lymphoma: This is a very slow-growing lymphoma that is usually curable. In Europe (but not in the United States), it is occasionally linked to an infection with Borrelia, the germ that causes Lyme disease. This lymphoma can occur at any age. It causes skin lesions that are red to purplish large pimples, plaques (raised or lowered, flat lesions), or nodules (bumps) on sun-exposed areas of skin, like the arms. There may be only a single lesion, but there can be more. When there are multiple lesions, there are usually only a few.
Primary cutaneous follicle-center lymphoma: This is the most common B-cell lymphoma of the skin. It tends to be slow growing. The early lesions are groups of red pimples, nodules, or plaques that form on the scalp, forehead or trunk. They are seldom found on the legs. Sometimes the pimples change into nodules. This is typically a disease of middle-aged adults. The lymphoma is very sensitive to radiation therapy, and most patients with this disorder have an excellent outlook.
Primary cutaneous diffuse large B-cell lymphoma, leg type: This is a rapidly growing lymphoma that begins as large nodules, mainly on the lower legs. It occurs most often in older people, and is more common in women than men. In some patients, this lymphoma spreads to lymph nodes and internal organs, causing serious problems. These lymphomas often require more intensive treatment. The outlook is best if there is only one lesion at the time of diagnosis.
Primary cutaneous diffuse large B-cell lymphoma, other (non-leg): These rare skin lymphomas are similar to large B-cell lymphomas that appear on the legs, except they develop on other sites in the body. They can also develop inside blood vessels under the skin. They tend to require intensive treatment, and the outlook is best if they are limited to only the skin.
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