CD4 and mycosis fungoides: Mycosis fungoides (MF) is the most common type of primary cutaneous lymphoma(PCL), a malignant disease initially affecting the skin.[1,2] MF is characterized by a clonal expansion of atypical CD4+ skin-homing T lymphocytes.[3] MF has an indolent and prolonged clinical course over years or sometimes decades, progressing from patches to more infiltrated plaques and eventually to tumors.