News, Views, and Reviews. Myocosis Fungoides-An Update on a Non-Mycotic Disease
July 2013 | Volume 12 | Issue 7 | Feature | 825 | Copyright © 2013
Joy Makdisi BS and Adam Friedman MD FAAD
Mycosis fungoides was first described in 1806 by the French physician Jean Louis Alibert in a patient whose skin lesions developed into mushroom-like tumors. Though it is not an infectious disease, it was termed mycosis fungoides (MF) due to its fungating appearance.1 In 1870, Bazin further described MF, proposing the three classical stages of the cutaneous disease: patch, plaque, and tumor.2 The term cutaneous T-cell lymphoma (CTCL) was first utilized in 1975 by Lutzner et al to describe a group of malignant infiltrative disorders of the skin including MF and Sézary syndrome.3 CTCLs comprise a spectrum of extranodal non-Hodgkin’s lymphomas that are characterized by primary cutaneous involvement of a dominant clonal T-cell.4 As molecular biology and immunohistochemistry techniques have become more developed, CTCL has become understood to be a heterogeneous assembly of disorders that vary with regards to clinical course, histopathology, therapeutic considerations, and prognosis.2,5 MF, a low-grade lymphoproliferative disorder, is the most common type of CTCL, comprising 54% of CTCLs.6,7 It is a rare, extranodal, non-Hodgkin’s lymphoma and is an epidermotropic neoplasm composed of CD4+ (helper) lymphocytes.8 Sézary syndrome is a related leukemic subtype of CTCL that presents with diffuse skin involvement as well as circulating tumor cells in the peripheral blood.8.
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Though MF is the most common subtype of CTCL, it is still a relatively uncommon malignancy. United States data is obtained from cancer registries that take part in the Surveillance, Epidemiology and End Results (SEER) program. The most recent data reported that the annual incidence is 4.5 cases/million or 0.36 per 100,000 person-years.9 Additional data indicates that the incidence of MF may be increasing, however this rise may be due to enhanced diagnosis and/or reporting instead of a true increase in incidence.2,9
MF more commonly affects older adults, with a median age at diagnosis of 55-61 years; it is rarely seen before the age of 30.10-12 There has been some recognition that MF may arise in children and adolescents, though it remains less common.13,14 The pediatric incidence may be under-reported because physicians are more hesitant to biopsy and because data on younger patients may not be analyzed separately.2
The incidence of MF is higher among men, with the sex difference increasing with age.15,16 The male-female ratio of MF across several large series was found to range from 1.7-2.2.10,11,17
The incidence of MF is higher among black patients than among white patients in all age groups, and is lower for Asians as compared to whites; however, racial differences diminish with age.9,15 A 1999 US study indicates that there is a lack of population data about Asian and American Indian sub-groups; no data is reported for Hispanic groups.9 Older data for Los Angeles County indicates that Hispanics had a lower incidence of MF as compared to whites.18
There is considerable geographic variation in incidence, correlating with factors such as high family income and high percentage of population with advanced degrees.15 In addition, there is an association between incidence and high physician density. This suggests that a detection bias may be partially responsible for the geographic differences seen.2,17
Finally, as definitions of ICD-O codes have changed, shifts in the distribution of CTCLs within subcategories have made it more difficult to assess incidence tendencies for sub-types of CTCL, such as MF.15 It has been suggested that these redistributions may have contributed to the apparent stabilization in the incidence of MF since the 1980’s.9
Though the exact pathophysiologic mechanism of MF remains unclear, several risk factors have been identified. Occupational exposure has been suggested as a potential risk factor for the development of MF.2 A study by Cohen et al reported a relative risk of 4.3 for MF in patients in industrial employment. Additional studies in textile, machinery, chemical, and service industries were incongruous about the correlation between exposure and MF risk.19-21
Genetics may play a partial role in the etiology of MF.2,16,19 In a US study, skin disease in a first-degree relative was noted in up to 26% of MF patients, and 5% of patients noted an affected parent.16 Though a small regional study found an association between MF and a history of malignancy, a subsequent more extensive study demonstrated no association, likely negating the previous findings. Morales et al suggest this discrepancy may be due to Berkson’s bias.2,22,23
Several other factors have been examined, including history of atopic disease and antecedent skin disease, viral and fungal infection, smoking and alcohol history, drug use, and ultraviolet exposure.21,22 The data is limited, but thus far an association has not been proven for these factors.