Mycosis fungoides on a young Hispanic male patients arm. Mycosis fungoides (cutaneous T-cell lymphoma) is a type of non-Hodgkin lymphoma, a rare cancer of the lymphoid tissue that primarily affects the skin. The disease progresses from itchy dermal patches to purple-coloured tumours, which eventually ulcerate. Severe cases of mycosis fungoides are fatal, although remission may be gained with anticancer drugs. Despite the name it does not involve fungal infection. The cause of the disease is unknown.