Mycosis fungoides is a rare type of blood cancer that starts in the skin. It involves T cells, which are a type of white blood cell. It is the most common form of cutaneous T-cell lymphoma.

Mycosis fungoides usually starts as a rash on the skin that does not go away. The rash may be itchy and can appear anywhere on the body.

Over time, the rash can turn into patches or plaques of raised skin that are scaly or crusted, and then tumors develop. The cancer can also spread and affect the blood, lymph nodes, and internal organs.

There is no cure for mycosis fungoides unless it is diagnosed in its earliest stage. However, treatments can help improve a person’s outlook and quality of life in later stages of the disease. Options include chemotherapy, radiation therapy, and newer options such as immune checkpoint inhibitors.

This article discusses mycosis fungoides, including pictures and symptoms by stage.

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Mycosis fungoides is a type of cutaneous T-cell lymphoma. It is a rare blood cancer that starts in T cells in the skin. Doctors may also call it granuloma fungoides.

In mycosis fungoides, cancerous cells first appear on the skin as a rash or patch. Over time, they can grow into tumors. In later stages, it can spread to other parts of the body, such as the lymph nodes, liver, and other organs.

Not everyone with mycosis fungoides experiences all of these symptoms. Some people may only have a rash without progressing to the next stages.

Sézary syndrome also involves cancerous lymphocytes and affects the skin. However, in mycosis fungoides, the cancerous T-cell lymphocytes are in the skin, while in Sézary syndrome, the cells also circulate in the blood. These cells are known as Sézary cells.

Doctors describe the progression of both mycosis fungoides and Sézary syndrome using the same staging system. They are:

  • Stage 1A: The affected areas cover less than 10% of the skin. A small number of Sézary cells may be present.
  • Stage 1B: The affected areas cover more than 10% of the skin. Some Sézary cells may be present.
  • Stage 2A: The affected areas cover any amount of the skin. Lymph nodes have abnormalities but are not cancerous. Some Sézary cells may be present.
  • Stage 2B: One or more skin tumors are 1 centimeter or larger. Lymph nodes have abnormalities but are not cancerous. Some Sézary cells may be present.
  • Stage 3: More than 80% of the skin is affected. Lymph nodes have abnormalities but are not cancerous.
  • Stage 4A1: This stage is now Sézary syndrome. Any amount of skin is affected, and 80% or more is inflamed. Lymph nodes have abnormalities but are not cancerous. A person has high numbers of Sézary cells in the blood.
  • Stage 4A2: This stage is now Sézary syndrome. Any amount of skin is affected, and 80% or more is inflamed. Lymph nodes are highly abnormal or cancerous. A person has high numbers of Sézary cells in the blood.
  • Stage 4B: Cancer has spread to other organs, such as the spleen or liver. Any amount of skin is affected, and 80% or more is inflamed. Lymph nodes are highly abnormal or cancerous. A person has high numbers of Sézary cells in the blood.

Cancerous T cells can spread to other parts of the body at any stage of mycosis fungoides, but it happens most often at the tumor stage.

The symptoms of mycosis fungoides vary by stage. A person may experience the following:

  • Stage 1: An itchy rash appears on the skin. The patches may extend over the trunk and extremities and resemble other rashes, such as psoriasis, lichen planus, or eczema. A person may also have insomnia.
  • Stage 2: Circular plaques develop that may be red, purple, or brown. They may gradually enlarge and join together. The lymph nodes may become inflamed.
  • Stage 3: This is the tumor or fungoid stage. Mushroom-like tumors appear that are rounded and bluish or red-brown. The skin thickens, and lower layers may become necrotic.
  • Stage 4: The cancer spreads throughout the body, causing a general feeling of illness, weakness, fever, weight loss, and anemia. There may be gastrointestinal ulcers and an enlarged liver and spleen.

Cancer occurs when cells change and begin to grow, multiply, and die in an atypical way. In mycosis fungoides, this happens in a specific type of T cell. These cells become attracted toward the skin and begin accumulating there, resulting in rashes or tumors.

Although the symptoms appear on the skin, it is not actually skin cells that have become cancerous, but T cells in the blood.

Scientists do not know why some people develop this condition. However, most people with the condition have one or more chromosomal differences that may explain it.

Chromosomes are thread-like structures inside cells that consist of DNA. People with mycosis fungoides often have more or less genetic material than is typical, or their genes appear in a different order.

Other potential risk factors include:

  • exposure to carcinogenic substances
  • certain bacterial or viral infections, such as human T-lymphotropic virus type 1
  • high levels of specific cytokines, which are involved in inflammation

Mycosis fungoides is also more common in adults over the age of 40 and in males.

A dermatologist can often diagnose mycosis fungoides based on the appearance of the skin rash. For a definitive diagnosis, though, a doctor will need to perform a biopsy.

A biopsy involves taking a small skin sample to look at under a microscope. A pathologist will also do tests to see whether the cells are cancerous.

If the biopsy shows mycosis fungoides, a doctor may order further blood and imaging tests to stage the disease and to look for any signs it has spread, or metastasized, in other parts of the body.

There are various treatments for people with mycosis fungoides.

Topical treatments

Topical treatments target the rashes and lesions specifically. Doctors may suggest:

  • topical corticosteroids
  • topical chemotherapy
  • bexarotene, a type of retinoid

Procedural treatments

These treatments aim to cure or improve mycosis fungoides. They include:

  • Photodynamic therapy: This therapy uses a drug and a laser light to kill cancer cells. The light activates the drug and only affects cancer cells. An example is psoralen and ultraviolet A (PUVA) therapy, which uses the drug psoralen with UVA light.
  • Radiation therapy: Radiation therapy uses high energy X-rays or other radiation to kill cancer cells or slow their growth. Doctors may also use it as palliative therapy to relieve symptoms.
  • Extracorporeal photopheresis: This treatment involves drawing blood from the body and sensitizing T cells to UVA light. This allows doctors to damage the cancerous cells with UVA light. Doctors then put the blood back into the patient’s body.

Systemic treatment

Systemic treatments affect the whole body. Doctors may use them to cure the condition, or they may use them to slow the progression of the disease. They include:

  • Chemotherapy: Chemotherapy involves using drugs that kill cancer cells or stop them from dividing. Mycosis fungoides tends not to respond much to chemotherapy, but doctors may use it with other therapies. They may also use chemotherapy as part of palliative care.
  • Immunotherapy: Immunotherapy is a treatment that harnesses the person’s own immune system to fight cancer. One example is immune checkpoint inhibitor therapy. It is a newer treatment still undergoing trials.
  • Oral retinoids: Oral retinoids and rexinoids are forms of vitamin A. These drugs inhibit the growth of tumors.
  • Allogeneic stem cell transplant: This involves doctors transplanting stem cells from a healthy donor into a person with cancer. Stem cells have the potential to become any type of cell, so they can become healthy T cells and replace the cancerous ones. Experts recommend this treatment for advanced or difficult-to-control mycosis fungoides.

Mycosis fungoides has no cure unless doctors can diagnose it in the earliest stage. At this point, people have a 95% survival rate over 10 years, according to a 2022 research review. However, people with advanced mycosis fungoides have a survival time of 3–4 years on average.

If a person has extra-cutaneous disease, meaning the cancer has spread beyond the skin, they have an average survival time of 18 months.

If mycosis fungoides returns after treatment, it is known as a relapse. The cancer may come back in the same area as the original tumor or in a new area.

Relapses are common. The cancer can be more aggressive if this occurs.

If mycosis fungoides comes back, doctors may revise their earlier approach based on the person’s wishes and goals. A person may want to continue with treatment to prolong their life as much as possible, while others may prefer to focus on symptom relief and supportive care.

Mycosis fungoides is a rare type of cancer that starts in the skin. At first, it causes an itchy rash on the skin. In later stages, the rash may develop into plaques or tumors.

The outlook for people with mycosis fungoides is variable depending on the stage of the disease. It is possible to cure the condition if doctors diagnose it in the first stage. In later stages, treatment tends to focus on prolonging life and alleviating symptoms.