Mycosis fungoides is a rare, persistent, very slow-growing non-Hodgkin lymphoma. Most people who develop it are older than 50. It originates from mature T cells (T lymphocytes) and first affects the skin. Mycosis fungoides starts so subtly and grows so slowly that it may not be noticed initially. It causes a long-lasting, itchy rash—sometimes a small area of thickened, itchy skin that later develops nodules and slowly spreads. In some people, it develops into a form of leukemia (Sézary syndrome). In other people, it progresses to the lymph nodes and internal organs. Even with a biopsy, doctors have trouble diagnosing this disease in its early stages. However, later in the course of the disease, a biopsy shows lymphoma cells in the skin.
The thickened areas of skin are treated with a form of radiation therapy called electron beam therapy or with sunlight and corticosteroids applied to the skin. Mechlorethamine applied directly to the skin can help reduce the itching and size of the affected areas. Interferon drugs can also reduce symptoms. If the disease spreads to lymph nodes and other organs, chemotherapy may be needed. On average, people live 7 to 10 years after the diagnosis is made, but survival varies widely depending on how far the cancer has spread. Treatment does not cure the disease but slows it down even further.