Mycosis fungoides (MF) and Sézary syndrome (SS) are the most common subtypes of cutaneous T cell lymphoma (CTCL) .
- MF is a mature T cell non-Hodgkin lymphoma with presentation in the skin but with potential involvement of the nodes, blood, and viscera . Skin lesions include patches or plaques that may be localized or widespread, tumors, and erythroderma.
- SS is defined as a distinctive erythrodermic CTCL with a leukemic involvement of malignant T cells clonally matching that in the skin.
This group of disorders differs from other primary cutaneous T cell lymphomas by virtue of unique clinical features and histopathology [3,4]. This topic review will discuss the clinical features, diagnosis, and staging of MF. The diagnosis of SS and the management of these disorders are discussed separately. (See "Clinical presentation, pathologic features, and diagnosis of Sézary syndrome" and "Treatment of early stage (IA to IIA) mycosis fungoides" and "Treatment of advanced stage (IIB to IV) mycosis fungoides and Sézary syndrome".)
The cause of MF is unclear. Current hypotheses include genetic and epigenetic abnormalities [5-9]. Although environmental and occupational exposure to solvents and chemicals has been implicated in the etiology of the disease, a large case-controlled study failed to support this hypothesis . An infectious etiology for MF has been suggested, but no relation has been confirmed . Human T-lymphotropic virus type I (HTLV-I) has been reported in the peripheral blood or cutaneous lesions of some patients with MF [12,13]. However, an equal number of studies have evidence against a role of HTLV-I [14,15].
- Clonal abnormalities — Clonal abnormalities have been identified in tumor cells, mostly deletions and translocations involving several different chromosomes or chromosomal segments [16,17]. Growing evidence from gene expression profiles and microRNA profiling suggests that MF and Sézary syndrome (SS) may be separate entities with differing pathogenesis [18-21]. Comparative genomic hybridization has identified chromosomal abnormalities that occur in both MF and SS and abnormalities that are present in either MF or SS, but not both [22-24]. The pathogenesis of SS is presented separately. (See "Clinical presentation, pathologic features, and diagnosis of Sézary syndrome", section on 'Pathogenesis'.)