is a disease in which T-cell lymphocytes (a type of white blood cell) become malignant (cancerous) and affect the skin. This condition is one of the most common types of T-cell lymphoma. Mycosis fungoides is characterized by a scaly, red rash that develops on the skin, particularly on areas that are not usually exposed to the sun. The rash may last for months or years without causing any symptoms. Over time, a thin, reddened, eczema-like rash may develop, followed by thickened, red patches of skin. Finally, tumors form which may develop into ulcers and become infected. Mycosis fungoides is difficult to cure. Treatment is usually palliative, with the intention of relieving symptoms and improving the quality of life. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.