Mycosis fungoides is an epidermotropic cutaneous T-cell lymphoma, a type of extranodal non-Hodgkin lymphoma, characterized by a proliferation of small to medium-size T lymphocytes with cerebriform nuclei with skin as their primary site.

• Cutaneous T-cell lymphoma
• MF

• •In the U.S., the annual incidence of cutaneous lymphomas is 0.6 to 1.0 cases per 100,000, with mycosis fungoides (MF) constituting about 50% of the cases.
• •MF affects more males than females (2:1), and majority of patients are White (70%).
• •Median age of diagnosis is 55 to 60 yr, but it can be seen in young adults and children.

• •MF presents with pruritic skin lesions of varying sizes that may manifest as erythematous patches, plaques, or tumors (Fig. E1 ), affecting virtually any body surface.
• •Clinical course is typically indolent with slow progression over years and, in some cases, over decades.
• •Skin lesions in MF may evolve over time but initially start as scaly patches, developing into infiltrative plaques and eventually to tumors.
• •Patients may show a combination of patches, plaques, and tumors at the same time. If only tumors are present, without preceding or concurrent patches or plaques, a diagnosis of MF is highly unlikely, and another type of cutaneous T-cell lymphoma should be considered.
• •Scaling often occurs on patch and plaque lesions.
• •Rarely, lesions are atrophied and dyspigmented.
• •Some patients develop erythroderma later in the course of the disease.
• •Lesions can be intensely pruritic, which can significantly impact a patient’s quality of life.
• •The initial skin lesions have predilection for the buttocks and other sun-protected areas (“bathing suit” areas).
• •Sézary syndrome (SS) is considered in patients with erythroderma, circulating T cells, and with or without associated lymphadenopathy.

Staging (Table E1 ) is helpful in guiding therapy and has prognostic value.

The lesions of mycosis fungoides are classified into four tumor (T) groups:

• •T1: Patches and plaques affecting less than 10% of body surface area
• •T2: Patches and plaques affecting more than 10% of body surface area
• •T3: Presence of tumors (i.e., raised, dome-shaped lesions >1 cm in diameter)
• •T4: Erythroderma affecting more than 80% of body surface area

Because patients with extensive MF lesions (T2 or T3 disease) can have substantial blood involvement in the absence of erythroderma, blood assessment is needed in these patients.¹

• •Stage IA is defined as a patch or plaque skin disease involving <10% of the skin surface area and with absence of blood involvement or with low blood tumor burden (<5% of Sézary cells in the peripheral blood).
• •Stage IB is defined as a patch or plaque skin disease involving ≥10% of the skin surface area (Fig. E2 ) with absence of blood involvement or low blood tumor burden (<5% Sézary cells).
• •Stages IIA & IIB are defined by the presence of tumors with or without clinically abnormal peripheral lymph nodes with absence of blood involvement or low blood tumor burden. In approximately 5% of cases of MF, the presentation may be a diffuse, painful, pruritic erythroderma with Sézary cells (Fig. E3 ) in the peripheral blood (known as Sézary syndrome) (Fig. E4 ).
• •Stage III disease is defined by the presence of generalized erythroderma from the spread of cancer cells through the skin but not yet to the lymph nodes.
• •Stage IVA disease is defined by a lymph node biopsy showing large clusters of atypical cells, more than six cells, or total effacement by atypical cells.
• •Stage IVB disease is defined by the presence of visceral involvement.

Several etiologies have been postulated for MF. There is a supporting role of the skin microenvironment in the pathogenesis, as MF is thought to arise in the background of chronic inflammation. Extravasation and migration of malignant T cells are facilitated by chemokines, cytokines, and adhesion molecules. Th1 and Th2 cytokines are both involved in different stages of the course of MF.

• •Contact dermatitis
• •Atopic dermatitis
• •Nummular dermatitis
• •Parapsoriasis
• •Superficial fungal infections
• •Drug eruptions
• •Psoriasis
• •Photodermatitis
• •Alopecia mucinosa
• •Lymphomatoid papulosis

Any patient who is suspected of having MF should have a staging workup. Prognosis in patients with mycosis fungoides depends on the type of skin lesions and the extent of disease. The workup should focus on:

• •Complete physical examination:
  1. 1.The type of skin lesion and the extent of skin involvement of the body (e.g., skin involvement is >10% or <10% of the skin surface)
  2. 2.Identification of palpable lymph nodes (especially those >1.5 cm in largest diameter)
  3. 3.Identification of organomegaly (e.g., lungs, liver)
• •Skin biopsy:
  1. 1.Biopsy of the most indurated area (multiple skin biopsies are often required)
  2. 2.Immunophenotyping
  3. 3.Evaluation for clonality
• •Blood testing:
  1. 1.CBC with differential, liver function tests, lactate dehydrogenase, chemistry
  2. 2.T-cell receptor gene rearrangement
  3. 3.Determination of Sézary cell count and/or flow cytometry
• •Radiologic tests: Depending on the stage of the disease, chest x-ray examination; ultrasound; and computed tomography scan of the chest, abdomen, and pelvis alone, with or without fluorodeoxyglucose PET scan
• •Lymph node biopsy:
  1. 1.Excisional biopsy of the largest lymph node should be done
  2. 2.If multiple nodes enlarged, order of preference is cervical, axillary, and inguinal areas
  3. 3.Histopathology, flow cytometry, T-cell receptor gene rearrangement

• •For dry, cracking skin, emollients (e.g., lanolin and petrolatum) are applied bid.
• •Moisturizing lotion (e.g., ammonium lactate) applied bid.
• •Topical antibiotics (e.g., bacitracin) are used on ulcerative tumors.

Treatment is guided by accurate disease staging and presence of limited vs. advanced disease.^2-4

The 10-yr rates of overall survival are as follows:

• •Stage I disease: 65% to 90%
• •Stage II disease: 35% to 50%
• •Stage III disease: 25% to 35%
• •Stage IV disease: 15% to 20%

The Cutaneous Lymphoma International Consortium analyzed 10 variables in 1275 patients and found four (stage IV, age >60 yr, large-cell transformation, and increased lactate dehydrogenase) were independent prognostic markers for a worse survival in advanced MF/SS patients. Combining these four factors, a prognostic index model was constructed that identified three risk groups across stages with significantly different 5-yr survival rates: Low risk (68%), intermediate risk (44%), and high risk (28%).⁶

Patient referral to a dermatologist with expertise in this entity. Oncology consultation is indicated in patients with more advanced disease.