Light micrograph of a section through a tumour (purple) in the skin of a patient with mycosis fungoides (cutaneous lymphoma). Mycosis fungoides is a type of non-Hodgkin lymphoma, a rare cancer of the lymphoid tissue that primarily affects the skin. The disease progresses through a mild form of eczema to a purple-coloured tumour, which eventually ulcerates. Severe cases of mycosis fungoides are fatal, although some remission may be gained with anticancer drugs. Despite the name it does not involve fungal infection. The cause of the disease is unknown.