Mycosis fungoides and the 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.
Blood cell development. A blood stem cell goes through several steps to become a red blood cell, platelet, or white blood cell.
In mycosis fungoides, T-cell lymphocytes become cancerous and affect the skin. In the Sézary syndrome, cancerous T-cell lymphocytes affect the skin and are in the blood.
Mycosis fungoides and the Sézary syndrome are types of cutaneous T-cell lymphoma.
Mycosis fungoides and the 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 possible 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 the 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 the Sézary syndrome is an advanced form of mycosis fungoides or a separate disease.
Tests that examine the skin and blood are used to detect (find) and diagnose mycosis fungoides and the Sézary syndrome.
The following tests and procedures may be used:
- Physical exam and 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.
Complete blood count (CBC). Blood is collected by inserting a needle into a vein and allowing the blood to flow into a tube. The blood sample is sent to the laboratory and the red blood cells, white blood cells, and platelets are counted. The CBC is used to test for, diagnose, and monitor many different conditions.
- Peripheral blood smear: A procedure in which a sample of blood is viewed under a microscope to count different circulating blood cells (red blood cells, white blood cells, platelets, etc.) and see whether the cells look normal.
- 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.
- Immunophenotyping: A process used to identify cells, based on the types of antigens or markers on the surface of the cell. This process may include special staining of the blood cells. It is used to diagnose specific types of leukemia and lymphoma by comparing the cancer cells to normal cells of the immune system.
- Immunogenotyping: A procedure in which a sample of DNA from a skin biopsy is studied to see if the genes for certain kinds of immune system proteins, such as the T-cell receptor or antibody proteins, are arranged in one pattern. Normally T-cell receptor genes and antibody genes are arranged in many different patterns. In mycosis fungoides and the Sézary syndrome, the genes are arranged in a single pattern.