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Mycosis fungoides is the most common form of cutaneous T-cell lymphoma, a slow-growing skin cancer managed with phototherapy, topicals, and specialist monitoring.
Mycosis fungoides is the most common type of primary cutaneous T-cell lymphoma (CTCL), a group of non-Hodgkin lymphomas that originate in the skin. Despite its name, the condition has no relation to fungal infections; the term reflects the mushroom-like appearance of tumour-stage lesions first described in the early 19th century. Mycosis fungoides is characterised by the clonal proliferation of mature, skin-homing CD4+ T-lymphocytes within the epidermis and dermis.
The disease typically follows an indolent clinical course, particularly in its early stages. It most commonly affects adults over the age of 50 and has a slight male predominance, with a male-to-female ratio of approximately 2:1. Early-stage mycosis fungoides confined to the skin carries a favourable prognosis, with many patients living for decades with appropriate management. However, a minority of cases may progress to advanced stages involving lymph nodes or internal organs.
The exact cause of mycosis fungoides remains unknown. The disease arises from the clonal expansion of malignant CD4+ T-lymphocytes that exhibit skin-homing properties, migrating to and persisting within the epidermis. The malignant T-cells accumulate in the skin over time, producing the characteristic patches, plaques, and tumours of the disease.
Several factors have been investigated as potential contributors, although no definitive causal agent has been identified:
Mycosis fungoides is not contagious and is not inherited in a simple genetic pattern. The condition is considered rare, with an estimated incidence of approximately 5 to 6 cases per million persons per year.
Mycosis fungoides typically progresses through three recognized clinical stages, though not all patients advance beyond the earliest phase:
Pruritus is a common symptom across all stages and can significantly affect quality of life. Some patients experience poikilodermatous changes, characterised by a combination of atrophy, telangiectasia, and mottled pigmentation. The disease may remain confined to a single stage for years or even decades.
The diagnosis of mycosis fungoides can be challenging, particularly in early stages when the clinical and histopathologic findings may be subtle and overlap with benign inflammatory dermatoses. Multiple skin biopsies may be required over time to establish a definitive diagnosis.
Key diagnostic components include:
Dermoscopy may provide additional diagnostic clues, including characteristic vascular patterns. Once a diagnosis is confirmed, staging evaluations may include blood work, imaging, and lymph node assessment to determine the extent of disease.
Treatment for mycosis fungoides is stage-dependent and follows a stepwise approach. Early-stage disease is typically managed with skin-directed therapies, while advanced-stage disease may require systemic treatment. The goals of treatment are to control symptoms, reduce skin lesions, prevent disease progression, and maintain quality of life.
Topical therapies are the mainstay of treatment for early-stage mycosis fungoides. Options include high-potency topical corticosteroids, topical nitrogen mustard (mechlorethamine), topical retinoids, and topical chemotherapeutic agents. These treatments target the malignant T-cells within the skin while minimizing systemic side effects.
Narrowband UVB phototherapy is a first-line treatment for patch-stage mycosis fungoides. Phototherapy induces apoptosis of the malignant T-cells in the skin and can produce complete or partial remission in a significant proportion of early-stage patients. PUVA (psoralen plus ultraviolet A) therapy may be considered for thicker plaques or more extensive disease. Regular treatment sessions are required, and maintenance therapy may help sustain remission.
Long-term surveillance is essential in the management of mycosis fungoides. Dermoscopic monitoring allows for serial assessment of skin lesions to detect changes in morphology or the emergence of new lesions. Regular skin cancer screening appointments provide comprehensive evaluation of the skin and support early detection of disease progression.
For patients with more advanced or refractory disease, systemic treatments may be considered. These include oral retinoids (bexarotene), interferon alfa, histone deacetylase inhibitors, and targeted immunotherapy agents. Total skin electron beam therapy (TSEBT) may be used for extensive skin involvement. Extracorporeal photopheresis is another modality used in the management of advanced cutaneous T-cell lymphoma. Treatment decisions for advanced disease are made on an individualized basis in consultation with a multidisciplinary oncology team.
Medical attention should be sought for persistent skin patches or plaques that do not respond to standard dermatitis treatments, particularly when lesions appear in sun-protected areas and are accompanied by pruritus. Because early-stage mycosis fungoides can mimic common inflammatory skin conditions such as eczema or psoriasis, a persistent rash that has been present for months or years without a clear diagnosis warrants evaluation by a specialist.
A referral from a family physician is typically required to access dermatology services at the Centre for Medical and Surgical Dermatology. Early diagnosis and management by a dermatologist with expertise in cutaneous lymphoma is associated with improved outcomes and quality of life.
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