Mycosis fungoides and Sézary syndrome are diseases in which lymphocytes (a type of white blood cell) become malignant (cancerous) and affect the skin.

Normally, the bone marrow makes blood stem cells (immature cells) that become mature blood stem cells over time. A blood stem cell may become a myeloid stem cell or a lymphoid stem cell. A myeloid stem cell becomes a red blood cell, white blood cell, or platelet. A lymphoid stem cell becomes a lymphoblast and then one of three types of lymphocytes (white blood cells):

• B-cell lymphocytes that make antibodies to help fight infection.
• T-cell lymphocytes that help B-lymphocytes make the antibodies that help fight infection.
• Natural killer cells that attack cancer cells and viruses.

In mycosis fungoides, T-cell lymphocytes become cancerous and affect the skin. When these lymphocytes occur in the blood, they are called Sézary cells. In Sézary syndrome, cancerous T-cell lymphocytes affect the skin and large numbers of Sézary cells are found in the blood.

Mycosis fungoides and Sézary syndrome are types of cutaneous T-cell lymphoma.

Mycosis fungoides and Sézary syndrome are the two most common types of cutaneous T-cell lymphoma (a type of non-Hodgkin lymphoma). For information about other types of skin cancer or non-Hodgkin lymphoma, see the following PDQ summaries:

• Adult Non-Hodgkin Lymphoma Treatment
• Skin Cancer Treatment
• Melanoma Treatment
• Kaposi Sarcoma Treatment

A sign of mycosis fungoides is a red rash on the skin.

Mycosis fungoides may go through the following phases:

• Premycotic phase: A scaly, red rash in areas of the body that usually are not exposed to the sun. This rash does not cause symptoms and may last for months or years. It is hard to diagnose the rash as mycosis fungoides during this phase.
• Patch phase: Thin, reddened, eczema-like rash.
• Plaque phase: Small raised bumps (papules) or hardened lesions on the skin, which may be reddened.
• Tumor phase: Tumors form on the skin. These tumors may develop ulcers and the skin may get infected.

Check with your doctor if you have any of these signs.

In Sézary syndrome, cancerous T-cells are found in the blood.

Also, skin all over the body is reddened, itchy, peeling, and painful. There may also be patches, plaques, or tumors on the skin. It is not known if Sézary syndrome is an advanced form of mycosis fungoides or a separate disease.

Tests that examine the skin and blood are used to diagnose mycosis fungoides and Sézary syndrome.

The following tests and procedures may be used:

• Physical exam and health history: An exam of the body to check general signs of health, including checking for signs of disease, such as lumps, the number and type of skin lesions, or anything else that seems unusual. Pictures of the skin and a history of the patient’s health habits and past illnesses and treatments will also be taken.
• Complete blood count with differential: A procedure in which a sample of blood is drawn and checked for the following:
  • The number of red blood cells and platelets.
  • The number and type of white blood cells.
  • The amount of hemoglobin (the protein that carries oxygen) in the red blood cells.
  • The portion of the blood sample made up of red blood cells.
  
• Sézary blood cell count: A procedure in which a sample of blood is viewed under a microscope to count the number of Sézary cells.
• HIV test: A test to measure the level of HIV antibodies in a sample of blood. Antibodies are made by the body when it is invaded by a foreign substance. A high level of HIV antibodies may mean the body has been infected with HIV.
• Skin biopsy: The removal of cells or tissues so they can be viewed under a microscope to check for signs of cancer. The doctor may remove a growth from the skin, which will be examined by a pathologist. More than one skin biopsy may be needed to diagnose mycosis fungoides. Other tests that may be done on the cells or tissue sample include the following:
  • Immunophenotyping: A laboratory test that uses antibodies to identify cancer cells based on the types of antigens or markers on the surface of the cells. This test is used to help diagnose specific types of lymphoma.
  • Flow cytometry: A laboratory test that measures the number of cells in a sample, the percentage of live cells in a sample, and certain characteristics of the cells, such as size, shape, and the presence of tumor (or other) markers on the cell surface. The cells from a sample of a patient’s blood, bone marrow, or other tissue are stained with a fluorescent dye, placed in a fluid, and then passed one at a time through a beam of light. The test results are based on how the cells that were stained with the fluorescent dye react to the beam of light. This test is used to help diagnose and manage certain types of cancers, such as leukemia and lymphoma.
  • T-cell receptor (TCR) gene rearrangement test: A laboratory test in which cells in a sample of blood or bone marrow are checked to see if there are certain changes in the genes that make receptors on T cells (white blood cells). Testing for these gene changes can tell whether large numbers of T cells with a certain T-cell receptor are being made.

Certain factors affect prognosis (chance of recovery) and treatment options.

The prognosis and treatment options depend on the following:

• The stage of the cancer.
• The type of lesion (patches, plaques, or tumors).
• The patient's age and gender.

Mycosis fungoides and Sézary syndrome are hard to cure. Treatment is usually palliative, to relieve symptoms and improve the quality of life. Patients with early stage disease may live many years.