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ChenDermatologist
ChenDermatologist
Dr. Chen Yi-Jia · Dermatology Notes
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Patient guide · Rare skin cancer Per TDA + Taiwan Hematology Oncology Society 2024 · Updated 2026-05-07

Cutaneous T-cell lymphoma (CTCL / MF)
Mycosis fungoides, Sézary syndrome, TNMB staging — complete breakdown

Cutaneous T-cell lymphoma (CTCL) is a rare non-Hodgkin lymphoma arising from malignant T cells in the skin. 75% are mycosis fungoides (MF); the remainder are Sézary syndrome and other variants. Early stages can be confused with eczema, psoriasis, or fungal infections, delaying diagnosis. This article covers staging (TNMB), early vs advanced features, and the treatment ladder (topical → phototherapy → systemic).

Note:This article is patient-education plus study notes. If CTCL is suspected, diagnosis requires dermatologist interpretation with skin biopsy + immunohistochemistry + T-cell receptor gene rearrangement. Treatment is at oncology level and requires multidisciplinary team decision-making (dermatology, hematology-oncology, radiation oncology).

What is CTCL?

Cutaneous T-cell lymphomas (CTCL) are mature T-cell malignancies originating in the skin. Per WHO-EORTC 2018/2022 classification, the major subtypes are mycosis fungoides (MF, ~60% of CTCL), Sézary syndrome (SS, ~3%), and CD30+ lymphoproliferative disorders (~25%; LyP and pcALCL). MF is typically extremely indolent, with 10-year survival > 80-90% in early stages (IA-IIA).

Classic MF Stages

  • Patch: flat, scaly, erythematous lesions on sun-protected sites (buttocks, inner thighs, trunk); often misdiagnosed as eczema, parapsoriasis, tinea, drug eruption
  • Plaque: raised, indurated lesions with clearer borders; ddx with psoriasis, lichen planus
  • Tumor: nodules, ulcers, "leonine facies"
  • Erythrodermic MF (eMF): ≥ 80% BSA erythema, often overlapping with SS

Diagnostic Algorithm (ISCL 2005)

Early MF is notoriously difficult to diagnose. The ISCL algorithm scores clinical, histopathologic, immunophenotypic, and molecular criteria:

  • Clinical: persistent/progressive patches, non-sun-exposed sites, asymmetry, atrophy/poikiloderma
  • Histology: epidermotropism, Pautrier microabscesses, lining of basal layer by lymphocytes
  • Immunophenotype: loss of CD2/3/5/7, CD4:CD8 ratio > 6
  • Molecular: clonal TCR rearrangement

Score ≥ 4 strongly suggests MF. Multiple biopsies from different sites are often needed; a single negative biopsy does not exclude MF.

TNMB Staging (ISCL/EORTC 2007)

  • T (skin): T1 patches/plaques <10% BSA; T2 ≥10%; T3 tumors; T4 erythroderma ≥80%
  • N (nodes): N0-3 by histology/molecular involvement
  • M (visceral): M0-1
  • B (blood): B0-2; B2 (Sézary cells ≥1000/μL) defines SS

Early MF (IA-IIA) — Skin-Directed Therapy

  • Mid- to ultra-potent topical corticosteroids (Class I-II)
  • Topical mechlorethamine (Valchlor gel)
  • Topical 1% bexarotene gel
  • NB-UVB phototherapy (response 70-90%)
  • PUVA for thicker plaques and folliculotropic MF
  • Localized electron-beam radiotherapy for refractory single lesions
  • Total skin electron-beam therapy (TSEBT) for widespread plaques/erythroderma

Advanced MF / SS (Stage IIB-IVB) — Systemic

  • Oral bexarotene (Targretin) — RXR retinoid; manage hypothyroidism + dyslipidemia
  • Low-dose methotrexate 5-25 mg/wk
  • Interferon-α — immunomodulator
  • Brentuximab vedotin (Adcetris) — anti-CD30 ADC; ALCANZA: ORR4 56% vs 13%
  • Mogamulizumab (Poteligeo) — anti-CCR4 mAb; MAVORIC: median PFS 7.7 mo vs vorinostat 3.1 mo, especially for SS
  • HDAC inhibitors (vorinostat, romidepsin)
  • Pralatrexate, liposomal doxorubicin, gemcitabine
  • Allogeneic HSCT — only curative option for advanced MF/SS, 5-year OS ~30-40%

CD30+ Primary Cutaneous LPD

  • Lymphomatoid papulosis (LyP): recurrent self-resolving papules/nodules with malignant-appearing histology but excellent prognosis (5-yr survival ~100%); 5-20% develop another lymphoma. Watch & wait; recurrent disease may need low-dose MTX or UV.
  • Primary cutaneous anaplastic large cell lymphoma (pcALCL): solitary or multifocal CD30+ tumors; localized excision + radiotherapy → 5-yr survival 90%. Multifocal/extracutaneous disease: brentuximab vedotin.

Dupilumab / TNF-α and MF — Differentiation

TDA 2024 consensus highlight: emerging case reports describe MF/SS unmasked or aggravated after dupilumab (for AD) or TNF-α inhibitor (for psoriasis/IBD). The 2023 systematic review (Jfri et al, JAAD) compiled 14 cases. Likely "unmasking of pre-existing undiagnosed MF" rather than de novo induction. Before initiating biologics in long-standing refractory AD/psoriasis, perform skin biopsy if any MF-suggestive features are present:

  • Asymmetric distribution / non-sun-exposed dominance / poikiloderma
  • Poor response to standard topical (steroid / TCI) therapy
  • New onset of "AD/psoriasis" in adults > 50 years
  • Lymphadenopathy / abnormal blood counts / weight loss

Bottom Line — 5 Things

  1. MF is not a death sentence: early stage IA-IIA usually maintains near-normal lifespan
  2. Watch out for "treatment-resistant eczema": asymmetry, adult-onset, poikiloderma → biopsy
  3. Skin-directed first: topicals, phototherapy, local radiation give 70-90% response in early disease
  4. New drugs for advanced disease: brentuximab vedotin (CD30+) and mogamulizumab (SS) are the major 2018-2024 advances
  5. Differentiate before biologics: rule out MF before starting dupilumab / TNF-α / MTX in refractory AD/psoriasis