Tumor-node-metastasis-blood (TNMB) staging for MF is important in determining prognosis and treatment, and guidelines have been established. Stage I features only patches and plaques and is further divided into stage IA (< 10% of body surface area involvement) and stage IB (> 10% of body surface area involvement), based on the extent of skin involvement and the presence of patch-stage (T1a/T2a) or plaque-stage (T1b/T2b) disease. Stage IIA disease is characterized by patch/plaque stage disease (T1/T2) with clinically enlarged but architecturally preserved lymph nodes.
Stages I-IIA are limited or early-stage disease, with overall survival measured in decades. For patients with stage IA disease, survival is similar to that of age-matched controls. The prognosis of stage IB MF, as seen in this case, and of stage IIA is very good, with a median overall survival of greater than 11 years.
Advanced or late-stage disease consists of tumor-stage disease (T3), erythroderma (T4), nodal involvement characterized by partial or complete architectural effacement (N3), visceral metastases (M1), or significant leukemic involvement (B2). Median survival for late-stage disease is 1-5 years.
A definitive diagnosis of MF can be difficult because its clinical presentation is often nonspecific, particularly in the patch or plaque stage. The differential diagnosis for MF is extensive and includes eczema, psoriasis, drug reactions, and tinea corporis. In patients such as the one in this case, symptoms may be attributed to eczema or psoriasis for years before the correct diagnosis is made.
Histologic evaluation is essential for disease detection, particularly in the early phases. However, even the histologic appearance of MF may be nonspecific in the early stages; thus, diagnostic delay and multiple biopsies are common.
The histologic findings of MF varies according to the stage. Patch or plaque lesions consist of bandlike (lichenoid) infiltrates of enlarged lymphocytes with mildly atypical to hyperconvoluted cerebriform nuclei. These lymphocytes infiltrate the epidermis, which may be psoriasiform. The lymphocytes tend to align along the dermoepidermal junction and cluster together in the epidermis (Pautrier microabscesses). Perinuclear halos, or clear cytoplasm, around atypical lymphocytes are characteristic of MF. Papillary dermal fibrosis is also typical. As the lesions progress to the plaque and tumor stages, the cells often increase in size and number and become less epidermotropic. Tumors are characterized by nodular or diffuse infiltrates that involve the entire dermis and often the subcutaneous fat.
Immunohistochemical staining for CD2, CD3, CD5, and CD7 is useful for assessment of aberrant loss of T-cell antigen expression. The malignant lymphocytes of MF are typically CD3+, CD4+, and CD8- but often lose the expression of other pan–T-cell antigens. In most cases, demonstration of a significant population of CD4+ cells lacking CD2, CD5, and/or CD7 expression is highly specific (specificity of > 90%) for MF.
Confirmatory diagnostic tests include flow cytometric analysis of peripheral blood and detection of alpha/beta T-cell receptor gene rearrangements on skin tissue and peripheral blood. Flow cytometric analysis can identify neoplastic T cells, which are characterized as CD4+CD7- and/or CD4+CD26-.
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