14th July 2026

Cutaneous T-cell Lymphoma

Background

Cutaneous T-cell lymphoma (CTCL) is a group of uncommon disorders characterised by the accumulation of T lymphocytes in the skin. Mycosis fungoides (MF) and its leukaemic variant Sézary syndrome (SS) are subtypes of CTCL; MF behaves similarly to an indolent lymphoma, whilst SS is a much more aggressive form of the disease. 

Epidemiology

MF is a primary cutaneous non-Hodgkin’s lymphoma of T-cell origin and is the common subtype of CTCL. MF follows an indolent clinical course, typically with slow disease progression. The incidence of CTCL is on the rise; however, this may be attributed to improved rates of diagnosis.

Aetiology

Risk factors include HTLV virus, radiation exposure, severe atopic eczema, melanoma, and non-melanoma skin cancer. Occupational exposures to textiles and ceramics are also known risk factors. Anti-TNFα therapy can cause progression of cutaneous T-cell lymphoma.

Diagnosis

History and Examination

All patients should undergo a full skin examination to assess the body surface area (BSA) and type of lesions, as well as a lymph node examination and assessment for organomegaly/masses. Pruritus is commonly seen, particularly in those with SS.

Heterogeneous cutaneous manifestations include:

• Polymorphic patches/plaques
• Tumours and erythroderma 
• Hypopigmented lesions
• Hyperpigmentation (usually seen in younger children/adolescents)
• Granulomatous slack skin (resembles loose skin) 

SS is a rare leukaemic subtype of CTCL:

• Pruritic erythroderma
• Lymphadenopathy
• Sézary cells (clonally related neoplastic T-cells with cerebriform nuclei)

As both MF and SS may present with similar features, peripheral blood involvement is needed to differentiate the two. In order to definitively diagnose SS, the following is needed alongside Sézary cells:

• Absolute Sézary cell count of >1000/microlitre
• Expanded CD4+ T cell population resulting in CD4/CD8 ratio ≥10, CD4+/CD7- cells ≥30% or CD4+/CD26- cells ≥40%. 

MF typically presents in three stages, namely patch, plaque, and tumour stage. Initial presentation can mimic inflammatory skin conditions such as eczema and psoriasis. These typically progress to tumours and erythrodermic stages. In the few patients who progress straight to tumours, i.e., without patches or plaques, this is termed tumour d’emblee. A biopsy is needed to confirm diagnosis. 

Investigations include:

1. Bloods: FBC (normal or lymphocytosis), LFTs (usually normal), HIV (rule out HIV associated malignancy), LDH – strong predictor of poor prognosis (usually normal), beta 2 microglobulin, lymphocyte subsets CD4:CD8, HTLV serology (to differentiate HTLV-1-associated T-cell leukaemia/lymphoma from other T-cell leukaemias), Sézary cell count on blood film
2. Biopsy: skin, lymph nodes, bone marrow trephine biopsy
3. Immunohistochemistry: CD2, CD3, CD4, CD5, CD7, CD8, CD20, CD30 (tumour cells are typically CD3+, CD4+ and CD8-; CD7 is often lost); TCR gene analysis (if peripheral blood involvement suspected) 
4. Imaging: PET/CT for staging of disease

Clinical staging of CTCL is as follows:

Histology: epidermotropism is typically seen (characterised by T cells in the epidermis), Pautrier microabscesses (cluster of atypical lymphocytes)

Management

Aim to improve symptoms, cure is rarely achieved. 

Skin-directed therapies include topical medications: corticosteroids, imiquimod, chlormethine, retinoids (bexarotene), phototherapy, and localised radiotherapy

Systemic therapies include photopheresis, chemotherapy (methotrexate), and biological or immunological therapy (interferon-alpha)

First-line treatment: 

• Stage IA: 
  • 1st line – skin-directed therapies
  • 2nd line – systemic therapy
• Stage IB-IIA:
  • 1st line – skin-directed therapies
  • Predominantly plaque disease: PUVA or UVA1 
  • 2nd line – systemic therapy
• Stage IIB 
  • 1st line – skin-directed therapies AND systemic therapy, adjunct local radiotherapy 
• Stage III:
  • 1st line – skin-directed therapies AND systemic therapy AND antibiotics (due to increased risk of secondary infection)
• Stage IV: 
  • Systemic therapy, adjunct radiotherapy 
  • 2nd line – allogeneic haematopoietic cell transplant 

Complications

High likelihood: cutaneous ulceration 

Medium likelihood: cutaneous/systemic infections, secondary malignancy, therapy-related cutaneous malignancy (increased risk of non-melanoma and melanoma)

Low likelihood: complications related to erythroderma (heart failure, renal impairment), CNS involvement

References

• https://bestpractice.bmj.com/topics/en-gb/1025 
• https://ashpublications.org/blood/article/110/6/1713/24087/Revisions-to-the-staging-and-classification-of