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There are many types of skin lymphomas. Classifying them can be confusing (even for many doctors) because many of them are not very common.

The main system used to classify skin lymphoma is from the World Health Organization (WHO), which was last updated in 2016. It is based mainly on:

• Whether the lymphoma starts in T lymphocytes (T cells) or B lymphocytes (B cells)
• How the lymphoma looks under the microscope
• Whether certain proteins are on the lymphoma cells (based on lab tests)

T-cell skin lymphomas

Most skin lymphomas are T-cell lymphomas. These are sometimes called cutaneous T-cell lymphomas (CTCLs).

Mycosis fungoides: Nearly half of all skin lymphomas are mycosis fungoides (MF). MF can occur in people of any age, but most who get it are in their 50s or 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 (abnormal areas) 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 (called plaques). Because MF can be confused with other skin problems, it can be hard to diagnose at first. Several biopsies of the lesions might be needed before the diagnosis is confirmed.

Over time, MF can spread across the skin or invade lymph nodes and organs like the liver. In many people this disease grows slowly, but it can sometimes grow more quickly, especially in older people. Some people with MF go on to develop Sezary syndrome.

Rare variants of MF include folliculotropic MF, pagetoid reticulosis, and granulomatous slack skin.

Sezary syndrome (SS): This is often thought of as an advanced form of mycosis fungoides, but these are actually different diseases. In SS, most or all of the skin is affected, instead of just patches of skin. People with SS typically have a very itchy, scaly red rash that can look like a severe sunburn. This is called generalized erythroderma. The skin is often thickened. Lymphoma cells, called Sezary cells, can be found in the blood (as well as in the lymph nodes).

Whereas MF is usually slow growing, SS tends to grow and spread faster, and is harder to treat. People with SS also often have further weakened immune systems, which increases their risk of serious infections.

Adult T cell leukemia-lymphoma (ATLL): This rare type of T-cell lymphoma is more likely to start in other parts of the body, but it can sometimes be confined to the skin. It is linked to infection with the HTLV-1 virus (although most people infected with this virus do not get lymphoma). It is much more common in Japan and the Caribbean islands than other parts of the world. This lymphoma often grows quickly, but in some cases it advances slowly, or even shrinks on its own for a time.

Primary cutaneous anaplastic large cell lymphoma (C-ALCL): This lymphoma usually starts as one or a few tumors on the skin, which can vary in size. Some of these may break open (ulcerate).

Most people with this disease are in their 50s or 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 is a benign, slow-growing disease that often comes and goes on its own, even without treatment. In fact, some doctors think of it not as a lymphoma, but rather as an inflammatory disease that might progress to a lymphoma. But under a microscope, it has features that look like primary cutaneous ALCL.

Lymphomatoid papulosis often begins as several large pimple-like lesions that may break open in the middle.

This disorder is seen in younger people more often than other T-cell skin lymphomas, with an average age of around 45. Men get this disease more often than women.

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 another, more serious type of lymphoma.

Subcutaneous panniculitis-like T-cell lymphoma: This rare lymphoma invades the deepest layers of the skin, where it causes nodules (lumps) to form. Most often these are 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 outlook.

Extranodal NK/T-cell lymphoma, nasal type: This rare type of lymphoma can start in T-cells or in other lymphocytes known as natural killer (NK) cells. It typically starts in the nose or sinuses, but sometimes it can start in the skin. This lymphoma has been linked to infection with the Epstein-Barr virus (EBV), and is more common in Asia and Central and South America. It tends to grow quickly.

Primary cutaneous peripheral T-cell lymphoma, rare subtypes: This is a group of rare skin lymphomas that don’t fit into any of the above categories. There are several types.

• Primary cutaneous gamma/delta T-cell lymphoma develops as thickened plaques (raised lesions) or actual tumors, mainly on skin of the arms and legs, but sometimes in the intestines or lining of the nose. This type of lymphoma tends to grow and spread quickly.
• ?Primary cutaneous CD8+ aggressive epidermotropic cytotoxic T-cell lymphoma develops as widespread patches, nodules and tumors that often break open in the middle. This type of lymphoma can sometimes look like mycosis fungoides, but a biopsy can tell them apart. This lymphoma tends to grow and spread quickly.
• Primary cutaneous acral CD8+ T-cell lymphoma is very rare, and typically starts as a nodule on the ear, although it can also start on other parts of the body, such as the nose, hand, or foot. It tends to grow slowly and can often be cured with treatment.
• Primary cutaneous CD4+ small/medium T-cell lymphoproliferative disorder often starts as a single area of thickening of the skin or a tumor on the head, neck, or upper body. This disease tends to grow slowly and can often be cured with treatment.

B-cell skin lymphomas

These lymphomas are sometimes referred to as cutaneous B-cell lymphomas (CBCLs).

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 sometimes linked to an infection with Borrelia, the germ that causes Lyme disease.

This lymphoma can occur at any age, although it tends to occur more often in older adults. It appears as skin lesions that are red to purplish large pimples, plaques (raised or lowered, flat lesions), or nodules (bumps) on the arms or upper body. There may be only a single lesion, but there can sometimes be a few.

Primary cutaneous follicle center lymphoma: This is the most common B-cell lymphoma of the skin. It tends to grow slowly. The early lesions are groups of red pimples, nodules, or plaques that form on the scalp, forehead, or upper body. Less often they are found on the legs. Sometimes the pimples grow into nodules.

This type of lymphoma is typically found in middle-aged adults. It tends to respond well to radiation therapy, and most patients have an excellent outlook.

Primary cutaneous diffuse large B-cell lymphoma, leg type: This is a fast-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 people, this lymphoma spreads to lymph nodes and internal organs, causing serious problems.

These lymphomas often require more intensive treatment. The outlook is better if there is only one lesion at the time of diagnosis.