Cutaneous T-cell lymphoma

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Meet the patient

A 58-year-old man has been treated for 'eczema' for six years — scaly red-brown patches on his buttocks, hips, and lower back that never quite clear with topical steroids and slowly spread. Three biopsies were 'non-specific'. A fourth, taken from the most indurated plaque, finally shows epidermotropism with Pautrier microabscesses and a dominant T-cell clone.[1][4]

Two questions frame every CTCL stem: is this chronic eczema, or is it mycosis fungoides? — answered by the bathing-trunk distribution, the histology, and the TCR clone — and has it reached the blood? — answered by flow cytometry, because blood involvement converts indolent skin disease into Sezary syndrome and changes everything.[1][3]

One clone, four stages, one mimic to rule out — the spine of MF

Mycosis fungoides is the great mimicker of eczema and psoriasis, and the diagnosis is delayed an average of 3 to 6 years because of it. The malignant clone is a skin-homing CD4 positive central memory T cell — expressing the cutaneous lymphocyte antigen (CLA), the chemokine receptors CCR4 and CCR7, and the memory marker CD45RO — locked into the skin compartment by aberrant homing receptor expression.[1][3]

The disease marches through four stages, and the stage sets the prognosis and the treatment:[1]

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Patch stage (T1 under 10 percent BSA; T2 10 percent or more) is the earliest and most easily missed — flat, scaly, red-brown, variably atrophic patches favouring the bathing-trunk distribution (buttocks, hips, lower abdomen, lower back, breasts, axillae), areas typically spared by sun and by chronic eczema. Plaque stage brings raised, infiltrated, well-demarcated red-brown plaques, often with poikiloderma (atrophy, telangiectasia, mottled hyper- and hypopigmentation) — a strong clinical clue. Tumour stage (T3) brings dome-shaped red-brown or violaceous nodules that often ulcerate, and is a clinical red flag for large cell transformation. Erythroderma (T4) is generalised redness and scaling of more than 80 percent BSA — erythrodermic MF without blood involvement, or Sezary syndrome when the blood is involved.[1][4]

The classic trap: a chronic, treatment-resistant eczematous or psoriasiform eruption in a sun-protected bathing-trunk distribution persisting or progressing over years is MF until proven otherwise. The bathing-trunk distribution is the single strongest clinical clue — chronic eczema favours flexures, psoriasis favours extensors, and neither hides from the sun.[1][4]

Etymology for viva gold: mycosis fungoides — Alibert named it in 1806 for the mushroom-like (fungoid) tumours of late-stage disease; the mushroom metaphor is long obsolete but the name survived. Pautrier microabscesses honour Jean-Aimé Pautrier; Sezary cells honour Albert Sézary. Every eponym in this topic is a description of what the microscope or the blood film shows.[3]

Read the histology like the pathologist does

The defining histological hallmark of MF is epidermotropism — atypical lymphocytes within the epidermis without the surrounding spongiosis that defines eczema. Where clusters of atypical cells aggregate within the epidermis they form Pautrier microabscesses, the pathognomonic collection of three or more atypical lymphocytes in a small intraepidermal vesicle, seen in 20 to 30 percent of MF biopsies but diagnostic when present. The cells show cerebriform nuclei — small, hyperconvoluted, brain-like nuclei.[1][3]

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The immunophenotype is CD3 positive, CD4 positive, CD45RO positive, CD2 positive, with frequent aberrant loss of CD7 (up to 70 to 80 percent of cases) and CD26 (the dipeptidyl peptidase IV — loss of CD26 is the more sensitive marker for the Sezary cell population in blood). CD30 expression emerges with large cell transformation and defines the CD30 positive lymphoproliferative disorders.[3][5]

A single dominant T-cell receptor (TCR) gene rearrangement — most often of the beta or gamma chain — is detected by PCR or next-generation sequencing in 60 to 80 percent of patch MF, 80 to 90 percent of plaque MF, and over 95 percent of tumour MF and SS. This monoclonality distinguishes MF from reactive dermatitides in which the TCR repertoire is polyclonal. The same dominant clone can be tracked in skin, blood, and lymph node, allowing molecular staging.[6]

The classic trap: a single negative biopsy does not exclude MF — early patch histology is subtle and often read as 'chronic spongiotic dermatitis'. Multiple biopsies over time may be required, and a clinicopathological correlation conference — dermatologist and pathologist reviewing the slides side by side — is the gold standard for resolving equivocal cases. Never accept a single 'non-specific' biopsy in a chronic bathing-trunk eruption as the final answer.[4][6]

Sezary syndrome — the diagnostic triad that defines the leukaemic variant

Sezary syndrome is the leukaemic variant of CTCL, and its triad is one of the most examined in dermatopathology:[1][3][5]

1. Erythroderma — more than 80 percent BSA, red, scaling, intensely pruritic, often with ectropion, palmoplantar keratoderma, onychodystrophy, and patchy alopecia.
2. Generalised lymphadenopathy — often dermatopathic on biopsy, sometimes with partial or complete effacement.
3. Sezary cells in the peripheral blood — atypical cerebriform T cells (CD4 positive, CD7 and CD26 negative) at more than 1000 cells per microlitre, or a CD4 to CD8 ratio greater than 10, with a demonstrable T-cell clone by PCR.[1][3][8]

A monoclonal TCR gene rearrangement in the blood is required by the current WHO-EORTC and ISCL criteria and is the most reliable single laboratory marker of leukaemic involvement. Erythrodermic patients are at high risk of high-output cardiac failure, hypothermia, dehydration, electrolyte disturbance, and sepsis — the immediate causes of death in advanced disease.[8]

The classification and the variants that change the plan

CTCL is classified by the WHO-EORTC scheme (Willemze 2005, updated in the 2018 WHO classification), which integrates clinical, histological, immunophenotypic, and molecular criteria to define distinct disease entities rather than relying on histology alone. MF and SS dominate; the primary cutaneous CD30 positive lymphoproliferative disorders (lymphomatoid papulosis and primary cutaneous anaplastic large cell lymphoma) and several rarer variants complete the list.[6][7]

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Face-off — MF versus its closest mimics

MF mimics are legion, and recognising them prevents the two commonest errors: over-diagnosis of eczema as MF, and under-diagnosis of MF as chronic eczema.[1]

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The discriminator line: a dominant TCR clone plus epidermotropism without spongiosis plus a bathing-trunk distribution is MF; spongiosis and a polyclonal TCR is eczema; HTLV-1 serology positive is ATLL, not SS.[1]

Everyone forgets: in erythrodermic patients from HTLV-1 endemic areas (southern Japan, the Caribbean, West Africa, parts of South America and Iran), an HTLV-1 serology is mandatory. ATLL shares the erythroderma and circulating atypical lymphocytes of SS but is distinguished by positive HTLV-1 serology, frequent hypercalcaemia, lytic bone lesions, and the absence of the chronic psoriasiform prodrome of MF.[1]

TNMB staging — the framework that drives everything

The current staging system is the ISCL/EORTC revision of Olsen 2007, integrated into the AJCC 8th edition and used worldwide. The four components — T (skin), N (node), M (visceral metastasis), B (blood) — combine into clinical stages IA through IVA2 and IVB.[6][8]

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Investigations — staging the skin, the blood, the nodes, and the viscera

A structured workup guides staging, treatment selection, and prognosis. Take at least two skin biopsies from the most indurated or representative lesions, each sent for H and E, a CTCL-oriented immunohistochemistry panel (CD2, CD3, CD4, CD5, CD7, CD8, CD20, CD25, CD26, CD30, CD45RO, TIA-1, granzyme B, ALK-1), and PCR for TCR gene rearrangement (BIOMED-2 protocol). Serial clinical photographs and body charts document disease extent and response (mSWAT scoring).[2][6][8]

Blood investigations include a full blood count with differential (lymphocytosis, eosinophilia, Sezary cells on the film), peripheral blood flow cytometry quantifying the CD4 positive CD7 negative and CD4 positive CD26 negative populations, PCR for TCR gene rearrangement on peripheral blood defining the B0, B1, and B2 categories, serum LDH, soluble IL-2 receptor (sCD25), and IgE as prognostic markers, HTLV-1 serology in patients from endemic areas or with hypercalcaemia, and HIV serology in atypical aggressive disease.[8]

Imaging and tissue staging: palpate all peripheral node groups and perform excisional biopsy of any suspicious node (1.5 cm or more, hard, fixed, or enlarging) for histology and TCR clonality. Contrast-enhanced CT of neck, chest, abdomen, and pelvis for nodal and visceral staging in stage IIB or higher; FDG-PET/CT is more sensitive for nodal and visceral involvement in advanced disease. Bone marrow biopsy is not routine but is indicated in stage IV disease or before allogeneic transplantation.[2][6]

Management — stage-driven, skin-directed first for early disease

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The 2023 EORTC consensus (Latzka 2023) is the principal European guideline, broadly concordant with the US NCCN guideline. Treatment is stage-driven: skin-directed therapy for early disease, escalating to multimodal systemic therapy in advanced disease.[2][5][6]

Early MF (stages IA to IIA) — skin-directed therapy

Skin-directed therapy aims to clear the malignant clone from the skin while minimising systemic toxicity, and combination skin-directed therapy is more effective than single-modality treatment and may defer the need for systemic therapy for years.[1]

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Tumour stage (IIB) and CD30-positive disease

Total skin electron beam therapy (TSEBT) is the most effective single skin-directed modality for diffuse disease — a standard course of 12 Gy over 6 to 9 weeks, with higher doses (24 to 36 Gy) giving more durable remissions, overall response rates exceeding 90 percent in stage IB to IIA with complete response in 60 to 75 percent. Localised radiotherapy treats individual tumour nodules.[2][5]

Brentuximab vedotin — an anti-CD30 antibody-drug conjugate — is the standard of care for CD30 positive CTCL. The ALCANZA trial (Prince 2017) showed an objective response lasting at least 4 months (ORR4) of 56 percent versus 13 percent for physician's choice of methotrexate or bexarotene, with median progression-free survival of 16.7 versus 3.5 months. Peripheral neuropathy is the dose-limiting toxicity.[9]

Advanced disease — erythrodermic MF and Sezary syndrome (stage III to IVA1)

Extracorporeal photopheresis (ECP) is the first-line systemic treatment for Sezary syndrome — white cells collected by apheresis, exposed to 8-methoxypsoralen and UVA extracorporeally, and reinfused, inducing immunogenic apoptosis in malignant T cells. Best responses are in SS with a circulating clone, and ECP is often combined with bexarotene or interferon.[2][5]

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Mogamulizumab — a defucosylated humanised monoclonal antibody against CCR4 — is now preferred in Sezary syndrome. The MAVORIC trial (Kim 2018) showed superior progression-free survival over vorinostat in relapsed or refractory MF and SS, with a 37 percent response rate in Sezary syndrome. Drug rash (15 to 25 percent) is an important adverse effect and may mimic disease progression.[10]

Stage IVB (visceral) and refractory advanced disease: brentuximab vedotin for CD30 positive disease, mogamulizumab for blood-dominant disease, pralatrexate, gemcitabine, liposomal doxorubicin, and multi-agent chemotherapy (CHOP-like regimens) are options. Allogeneic haematopoietic stem cell transplantation is the only potentially curative option in advanced disease, considered in patients under 65 with chemosensitive disease and a suitable donor; reduced-intensity conditioning has reduced transplant-related mortality while preserving graft-versus-lymphoma effects. Newer therapies — cemiplimab (anti-PD-1) and PI3K inhibitors — have shown activity in early-phase trials.[2][5]

How patients with CTCL come to harm — the preventable list

• A chronic bathing-trunk eruption called eczema for years while mycosis fungoides spreads and transforms — the classic diagnostic delay, averaging 3 to 6 years.[4]
• A single negative biopsy accepted as the final answer in a chronic bathing-trunk eruption — repeat biopsies and clinicopathological correlation are needed.[4][6]
• Sepsis from secondary cutaneous infection — the leading cause of death in advanced CTCL, driven by Th2 cytokine skewing and skin-barrier loss. Staphylococcus aureus, Pseudomonas, and HSV reactivation are common.[1]
• Large cell transformation missed because a rapidly enlarging or ulcerating plaque was not re-biopsied.[5]
• Erythrodermic crisis — high-output cardiac failure, hypothermia, dehydration, and sepsis in T4 disease, needing ICU-level support.[1]
• ATLL missed in an erythrodermic patient from an HTLV-1 endemic area because HTLV-1 serology was not sent.[1]
• Systemic corticosteroids given before diagnosis — they mask the histology and should be avoided.[1]

Special populations

Paediatric and skin of colour. Hypopigmented MF is the commonest CTCL variant in children and in patients with skin of colour — hypopigmented scaly patches that are subtle and easily misdiagnosed as pityriasis alba, post-inflammatory hypopigmentation, or vitiligo. NB-UVB phototherapy is first-line; PUVA, bexarotene, systemic agents, and TSEBT are reserved for refractory disease. Biopsy of any persistent hypopigmented patch in a sun-protected distribution is mandatory. The prognosis is generally excellent.[1]

Pregnancy. CTCL may flare during pregnancy, though data are limited. NB-UVB is safe. Systemic retinoids (teratogenic), methotrexate (teratogenic), and interferon are generally avoided. ECP and TSEBT are acceptable. Decisions are made jointly with the obstetrician and haemato-oncologist.[1]

Elderly. The highest-incidence population; comorbidities frequently limit systemic options, so topical and phototherapy-based approaches are preferred, balanced against functional status and life expectancy.[1]

HIV-positive. CTCL may pursue a more aggressive course; antiretroviral therapy should be optimised. Distinguish from ATLL, which is HTLV-1 associated rather than HIV-associated.[1]

Prognosis, surveillance, and prevention

The prognosis varies dramatically with stage. Stage IA disease is largely curable with skin-directed therapy, with 10-year overall survival over 95 percent; stage IVB disease has a 5-year survival under 15 percent. Adverse prognostic factors are advanced T stage (T3, T4), blood involvement (B2), elevated LDH, elevated soluble IL-2 receptor, age over 60, large cell transformation, the folliculotropic variant, failure to achieve complete response after first-line therapy, and peripheral eosinophilia (a marker of Th2 cytokine skewing).[2][6]

There is no primary prevention for CTCL. The most important secondary preventive strategy is early biopsy of any chronic eczematous or psoriasiform eruption that does not respond to standard therapy, particularly in a sun-protected bathing-trunk distribution. Relapse is the rule — even in early-stage MF, relapse rates approach 30 to 50 percent within 5 years of clinical remission, so maintenance therapy (intermittent phototherapy, intermittent topical nitrogen mustard) is often continued indefinitely. Surveillance for second malignancies — non-melanoma skin cancer from phototherapy, Hodgkin lymphoma — is part of long-term follow-up.[1]

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Regional differences. The major guidelines are broadly concordant, but access varies: mogamulizumab and brentuximab vedotin are approved in the US, EU, UK, Japan, and Australia but not universally reimbursed; TSEBT and ECP are concentrated in tertiary centres. In India and other lower-resource settings, methotrexate and interferon are widely used first-line systemic agents for cost reasons. CTCL is under-reported in sub-Saharan Africa and Latin America, where pigmented skin may delay recognition and access to TCR PCR and flow cytometry is limited.[1]

The mantra, and the memory devices

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The mantra: bathing-trunk rash for years, epidermotropism with Pautrier microabscesses and no spongiosis, CD4 positive with loss of CD7 and CD26, a single TCR clone — biopsy early, treat skin-directed for early disease, escalate for blood.[1][6]

Ward-round test — three stems, thirty seconds each

Stem 1 — the eczema that would not clear (answer)

A 58-year-old man has scaly red-brown patches on his buttocks, hips, and lower back for six years, treated as eczema with topical steroids without resolution. Three biopsies were 'non-specific'. What is the diagnosis, what does the fourth biopsy need to show, and what confirms clonality? Model: The diagnosis is mycosis fungoides (patch stage) — the great mimicker of eczema, suggested by the sun-protected bathing-trunk distribution and the years of treatment resistance. The biopsy needs to show epidermotropism (atypical lymphocytes in the epidermis without spongiosis) and ideally Pautrier microabscesses — three or more atypical lymphocytes in a small intraepidermal vesicle. Immunohistochemistry shows CD4 positive cells with aberrant loss of CD7 and CD26, and PCR for the T-cell receptor gene rearrangement demonstrates a single dominant clone, confirming clonality. A clinicopathological correlation conference with the dermatologist and pathologist reviewing the slides together resolves equivocal cases.[1][4]

Stem 2 — the red man with lymph nodes (answer)

A 65-year-old man has diffuse erythroderma, generalised lymphadenopathy, intense pruritus, palmoplantar keratoderma, and ectropion. Peripheral blood flow cytometry shows a CD4 positive CD7 negative CD26 negative population with a CD4 to CD8 ratio of 15. What is the diagnosis, the triad, and the first-line systemic therapy? Model: The diagnosis is Sezary syndrome, the leukaemic variant of CTCL, defined by the triad of erythroderma (more than 80 percent BSA), generalised lymphadenopathy, and Sezary cells in the blood (CD4 positive CD7 negative CD26 negative cells at more than 1000 per microlitre, or a CD4 to CD8 ratio greater than 10, with a demonstrable TCR clone). First-line systemic therapy is extracorporeal photopheresis (ECP), often combined with bexarotene or interferon; mogamulizumab (anti-CCR4, MAVORIC) is preferred for refractory disease with a 37 percent response rate in SS. Send HTLV-1 serology to exclude adult T-cell leukaemia or lymphoma if the patient is from an endemic area. Watch for high-output cardiac failure, hypothermia, dehydration, and sepsis.[1][3][10]

Stem 3 — the plaque that started growing fast (answer)

A 60-year-old woman with known mycosis fungoides (stage IIB) has rapid enlargement and ulceration of a previously indolent plaque on her flank over six weeks. What has happened, what does the biopsy show, and what is the treatment? Model: This is large cell transformation — the most adverse biological event in MF, defined as large cells (4x a small lymphocyte) comprising more than 25 percent of the dermal infiltrate, often CD30 positive. Median survival post-transformation is approximately 2 years. The biopsy shows increased cellularity, large cells with vesicular nuclei and prominent nucleoli, frequent mitoses, and often CD30 positivity. Treatment escalates to systemic therapy — brentuximab vedotin for CD30 positive disease (ALCANZA), multi-agent chemotherapy, and evaluation for allogeneic stem cell transplantation, the only potentially curative option. Restage with CT or PET-CT. The lesson: re-biopsy any rapid change in a known MF lesion.[5][9]

References

1. [1]Lee H. Mycosis fungoides and Sézary syndrome Blood Res, 2023.PMID 37105561
2. [2]Latzka J, Assaf C, Bagot M, et al. EORTC consensus recommendations for the treatment of mycosis fungoides/Sézary syndrome - Update 2023 Eur J Cancer, 2023.PMID 37890355
3. [3]Larocca C, Kupper T. Mycosis Fungoides and Sézary Syndrome: An Update Hematol Oncol Clin North Am, 2019.PMID 30497668
4. [4]Sheern C, Levell NJ, Craig PJ, et al. Mycosis fungoides: a review Clin Exp Dermatol, 2025.PMID 40721285
5. [5]Weiner DM, Rook AH. Cutaneous T-cell Lymphoma Hematol Oncol Clin North Am, 2024.PMID 39079789
6. [6]Dummer R, Vermeer MH, Scarisbrick JJ, et al. Cutaneous T cell lymphoma Nat Rev Dis Primers, 2021.PMID 34446710
7. [7]Willemze R, Jaffe ES, Burg G, Cerroni L, Berti E, et al. WHO-EORTC classification for cutaneous lymphomas Blood, 2005.PMID 15692063
8. [8]Olsen E, Vonderheid E, Pimpinelli N, Willemze R, Kim Y, et al. Revisions to the staging and classification of mycosis fungoides and Sezary syndrome: a proposal of the International Society for Cutaneous Lymphomas (ISCL) and the cutaneous lymphoma task force of the European Organization of Research and Treatment of Cancer (EORTC) Blood, 2007.PMID 17540844
9. [9]Prince HM, Kim YH, Horwitz SM, Dummer R, Scarisbrick J, et al. Brentuximab vedotin or physician's choice in CD30-positive cutaneous T-cell lymphoma (ALCANZA): an international, open-label, randomised, phase 3, multicentre trial Lancet, 2017.PMID 28600132
10. [10]Kim YH, Bagot M, Pinter-Brown L, Rook AH, Porcu P, et al. Mogamulizumab versus vorinostat in previously treated cutaneous T-cell lymphoma (MAVORIC): an international, open-label, randomised, controlled phase 3 trial Lancet Oncol, 2018.PMID 30100375