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The annual incidence of MF and its variants is estimated at between 1/350,000 and 1/110,000, with classical MF accounting for about 80-90% of MF cases. The male to female ratio is 2:1. Classical MF predominantly affects adults and the elderly (median age at diagnosis: 55-60 years).

The disease first manifests by skin lesions consisting of flat patches, preferentially located asymmetrically on the buttocks and other sun-protected areas (lower trunk and thighs, and the breasts in women). Usually, patches are hypo- or hyperpigmented in dark-skinned individuals. Pruritus may be observed. In the later stages of the disease, infiltrated plaques and red-violet, dome-shaped tumors or generalized erythroderma may develop. Lymph nodes are the most frequent site of extracutaneous involvement. Visceral involvement (liver, lung, and bone marrow) may also occur.

The etiology remains unknown.

The diagnosis is based on clinical presentation and should be confirmed by a skin biopsy. Histological findings reveal a predominance of small pleomorphic (cerebriform) cells with epidermotropism. In most cases, immunohistology shows a memory T-helper phenotype (CD3+, CD4+, CD45Ro+, CD8- and CD45Ra-). CD30 and/or cytotoxic markers (i.e. TIA-1) may be positive in late stages, particularly in tumors with large cell morphology. In rare cases, cytotoxic markers may also be positive in early lesions. Molecular analyses reveal a clonal rearrangement of the T-cell receptor genes (this finding may be absent in early lesions). Staging investigations, including a computer tomography scan and/or positron emission tomography, should be performed in cases of advanced MF.

Differential diagnoses include inflammatory dermatoses (i.e. atopic dermatitis) in theearly stages of MF, and other large cell non-Hodgkin lymphomas (see this term) in later stages.

Treatment strategies during the early phases include mainly PUVA (photochemotherapy), interferon alfa-2a, retinoids (alone or in combination, and including new retinoids such as bexarotene), topical chemotherapy, topical steroids, and narrow-band UV-B (311 nm). Advanced disease can be treated by systemic chemotherapy, extracorporeal photopheresis, and/or radiotherapy (including total body electron beam irradiation). Other treatment modalities include new chemotherapeutic drugs (i.e. gemcitabine, fludarabine and pegylated doxorubicin), denileukin diftitox, alemtuzumab, and allogeneic stem cell transplantation. Many other treatment options have been proposed but have only been used in a limited number of patients.

The disease is slowly progressive (it may evolve over 10 to 30 years after the initial presentation). The prognosis depends on the stage at diagnosis.