Mycosis fungoides is an uncommon chronic T-cell lymphoma primarily affecting the skin and occasionally the internal organs.
Mycosis fungoides is rare compared with Hodgkin lymphoma and non-Hodgkin lymphoma. Unlike most other lymphomas, it is insidious in onset, sometimes appearing as a chronic, pruritic rash that is difficult to diagnose. It begins focally but may spread to involve most of the skin. Lesions are plaquelike but may become nodular or ulcerated. Eventually, systemic involvement of lymph nodes, liver, spleen, and lungs occurs, resulting in the advent of symptoms, which include fever, night sweats, and unintentional weight loss.
Diagnosis is based on skin biopsy, but histology may be equivocal early in the course because of insufficient quantities of lymphoma cells. The malignant cells are mature T cells (T4+, T11+, T12+).
Characteristic Pautrier microabscesses are present in the epidermis. In some cases, a leukemic phase called Sézary syndrome is characterized by the appearance of malignant T cells with serpentine nuclei in the peripheral blood.
Once mycosis fungoides has been confirmed, the stage (see Cotswold Modification of Ann Arbor Staging of Hodgkin Lymphoma and Non-Hodgkin Lymphoma) is determined by CT scan of the chest, abdomen, and pelvis and by bone marrow biopsy for blood or lymph node involvement. PET scan may also be used for suspected visceral involvement.
Most patients are > 50 yr at diagnosis; average life expectancy is 7 to 10 yr after diagnosis, even without treatment. However, survival rates vary markedly depending on stage at diagnosis. Patients who receive treatment for stage IA disease have a life expectancy analogous to that of similar people without mycosis fungoides. Patients who receive treatment for stage IIB disease survive for about 3 yr. Patients treated for stage III disease survive an average of 4 to 6 yr. Patients treated for stage IVA or IVB disease (extracutaneous disease) survive < 1.5 yr.
Electron beam radiation therapy, in which most of the energy is absorbed in the first 5 to 10 mm of tissue, and topical nitrogen mustard have proved highly effective. Plaques may also be treated with sunlight and topical corticosteroids. Systemic treatment with alkylating drugs and folic acid antagonists produces transient tumor regression, but systemic treatment is primarily used when other therapies have failed, after relapse, or in patients with documented extranodal or extracutaneous disease. Extracorporeal phototherapy with a chemosensitive drug has shown modest success. The adenosine deaminase inhibitors fludarabine and 2-chlorodeoxyadenosine show promise.