The cell of origin is a peripheral CD4+ T-lymphocyte. The immunophenotype of the neoplastic clone is CD3+ CD5+ CD4+ CD25-. Rare CD8+/CD4- cases were observed. Clonality studies demonstrated a monoclonal rearrangement of the T-cell receptor (TCR).

This is the most common form of cutaneous T-cell lymphoma. The annual incidence is around 0,3 cases per 100.000 in western countries. The median age at diagnosis is between 55 and 60 years, with a 2/1 male-to-female ratio.

The disease usually shows cutaneous patches, plaques, tumors or generalized erythroderma (Mycosis fungoides). Pruritus is a common symptom. Extracutaneous manifestations are more frequent in the presence of locally advanced disease (cutaneous tumors). The presence of erythroderma with circulating malignant cells (Sezarys cells) in the peripheral blood (PB) and in the bone marrow is consistent with the Sezarys syndrome, which is usually associated with lymphadenopathy. Other sites of involvement in disseminated disease include the lungs, the gastrointestinal tract, the liver and the central nervous system.

The tumor cell is a small lymphocyte with cerebriform nucleus, clumped chromatin and inconspicuous nucleoli. Epidermotropism by neoplastic CD4+ lymphocytes with the formation of Pautriers microabsecsses is the hallmark of the disease.

Phototherapy, radiation therapy and alpha interferon are the mainstay of treatment of cutaneous disease. Chemotherapy using various regimens was employed in cases displaying disseminated disease and in Sezarys syndrome with limited success.

The clinical stage is the most important indicator. Patient with limited cutaneous disease have an excellent prognosis. Patient with cutaneous tumours, generalized erythroderma, with Sezarys syndrome or extracutaneous disease usually have a short survival, ranging from 1 to 4 years.

The neoplastic cells have a low mitotic index and stimulation with phytohemagglutinin and interleuchin-2 IL-2) and IL-7 were used. The probability of detecting an abnormal clone largely correlates with the clinical stage, being very low in those patents with limited disease. Chromosome aberrations are detectable by conventional cytogenetic analysis in up to 60% of the cases with PB involvement (Sezary syndrome). Two recurrent structural changes were identified, namely der(1)t(1;10)(p2;q2) and der(14)t(14;15)(q;q?). Other recurrent abnormalities include loss of chromosome material at 1p22 and 1p36, involvement of chromosome 10 and 17p. The involvement of regions containing the T-cell receptor subunits, were observed rarely.