Mycosis Fungoides Cutaneous T Cell Lymphoma

Slide 1 · MYCOSIS FUNGOIDES

Cutaneous T-cell lymphoma

Cutaneous T-cell lymphoma: clinical course, biology and pathology

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Define mycosis fungoides within the cutaneous T-cell lymphoma spectrum.

Explain skin homing, clonality and the limits of molecular specificity.

Correlate patch, plaque and tumor lesions with microscopic patterns.

Interpret progression, Sézary syndrome and treatment context.

Slide 3 · A neoplasm of cells that migrate to skin

Mycosis fungoides is discussed among tumors of cellular migrants to skin.

The malignant lineage is lymphoid, not keratinocytic or melanocytic.

Its clinical appearance reflects tissue localization by transformed T cells.

T-cell lineage

Cutaneous homing

Skin-based lymphoma

Schematic (not histology)

Slide 4 · Cutaneous T-cell lymphoma is a spectrum

CTCL denotes multiple lymphoproliferative disorders involving the skin.

Mycosis fungoides is a defined clinicopathologic member of that spectrum.

Not every CTCL has the clinical evolution of mycosis fungoides.

Umbrella category

Several distinct presentations

Mycosis fungoides

Characteristic patches → plaques → tumors

Slide 5 · Core definition: A skin-homing helper T-cell lymphoma

The prototypic cells are CD4+ helper T lymphocytes with cutaneous tropism.

Lesions generally begin in skin; Overt extracutaneous disease is late.

Diagnosis rests on integration of clinical and pathologic patterns.

CD4+ • skin-homing • clonal

Slide 6 · An often prolonged cutaneous phase

Most patients have skin-localized disease for years.

This clinical indolence does not negate the neoplastic nature of the process.

A subset eventually develops tumors or extracutaneous disease.

Skin-only phase

Progressive lesions

Possible systemic spread

Time and progression are variable

Slide 7 · Age distribution does not exclude the diagnosis

Mycosis fungoides may develop at any age.

The disease as most common after 40 years of age.

In compatible lesions, age alone should not substitute for morphology.

Slide 8 · The trunk is a frequent site of disease

Early lesions commonly occur on truncal skin.

With broader cutaneous involvement, extremities, face and scalp may be affected.

Anatomic distribution is clinically useful but not independently diagnostic.

Trunk

Extremities

Face and scalp

Illustrative anatomic distribution

Slide 9 · Why CD4+ tumor cells accumulate in skin

Tumor cells express adhesion and chemokine-homing molecules.

Cutaneous lymphocyte antigen contributes to skin localization.

CCR4 is additionally highlighted in the lymphoid chapter.

Neoplastic CD4+ T cell

CLA / CCR4-associated homing

Epidermis + dermis

Schematic (not histology)

Slide 10 · Cutaneous lymphocyte antigen: Tissue targeting

Cutaneous lymphocyte antigen is associated with T-cell trafficking to skin.

Its expression provides a mechanistic link between lineage and site.

Skin localization reflects homing biology, not epithelial origin.

CLA → cutaneous localization

Slide 11 · CCR4 adds a chemokine-receptor component

The Chapter 13 discussion identifies CCR4 in skin-homing tumor cells.

Chemokine receptors participate in positioning T cells within tissues.

Cutaneous trafficking helps explain persistent skin lesions.

CCR4 expression

Homing interaction

Cutaneous retention

Schematic (not histology)

Slide 12 · Clonal T-cell receptor rearrangements

Mycosis fungoides cells represent a clonal T-cell population.

Clonal T-cell receptor gene rearrangements support shared lineage.

Clonality must be interpreted with clinicopathologic findings.

T-cell clone

Shared TCR rearrangement

Persistent lesion

Schematic (not histology)

Slide 13 · Genetic abnormalities are heterogeneous

Changes involving oncogenes and tumor-suppressor genes occur in CTCL.

Robbins does not identify a single mutation specific to this entity.

No one mutation should be portrayed as its defining genetic test.

Heterogeneous drivers

Multiple altered pathways

No disease-specific driver

Diagnosis remains integrated

Slide 14 · A characteristic clinical-pathologic constellation

Domain

Typical observation

Interpretive role

Clinical

Persistent patches, plaques or tumors

Pattern recognition

Histologic

Dermal band + epidermotropism

Tissue pattern

Biologic

CD4+ T cells; clonal rearrangement

Lineage support

Slide 15 · Skin lesions form a clinical continuum

The classic course is patch → plaque → tumor.

The phases are useful teaching categories, not mandatory uniform steps.

Different lesion morphologies may coexist in an individual.

PATCH

Flat + scaling

PLAQUE

Raised + scaling

TUMOR

Nodular growth

Schematic (not histology)

Slide 16 · Patch lesions: Subtle cutaneous disease

Flat erythematous or red-brown areas may show surface scale.

Early lesions may resemble eczema.

A persistent patch can precede more overt lymphoma for years.

Flat erythematous patch

Schematic (not histology)

Slide 17 · The premycotic phase can appear inflammatory

An eczematous presentation is typical of early mycosis fungoides.

Obvious nodal or visceral dissemination is absent at this phase.

Morphologic subtlety is a major reason for diagnostic uncertainty.

Clinical surface

Eczema-like patch

Underlying process

Neoplastic T cells in skin

Slide 18 · Plaque lesions: Raised and indurated

Plaques become elevated, scaling and erythematous.

Irregular outlines and firmness may emerge.

The appearance can be confused with psoriasis.

Raised indurated plaque

Schematic (not histology)

Slide 19 · Why plaque disease may mimic psoriasis

Both processes can produce red, thickened, scaling plaques.

The distinction therefore requires more than a descriptive skin examination.

In mycosis fungoides, atypical T-cell epidermotropism is informative.

Visible similarity

Erythema + scale + thickening

Decisive difference

Neoplastic lymphoid tissue pattern

Slide 20 · Tumor-stage lesions are distinct from plaques

Advanced lesions may form nodules with a fungating surface.

Deep dermal growth contributes to nodule formation.

Tumor development is associated with aggressive clinical behavior.

Nodule with protruding growth

Schematic (not histology)

Slide 21 · Ulceration can complicate advanced lesions

Plaques or tumor nodules can ulcerate.

Ulceration is a feature of some lesions, not a required diagnostic sign.

The microscopic and clinical context must still establish the entity.

Ulcerated advanced lesion

Schematic (not histology)

Slide 22 · Cutaneous distribution may become extensive

Disease may expand beyond the trunk.

Extremities, face and scalp can eventually be affected.

Anatomic extension increases the need for systematic skin assessment.

Truncal lesions

Additional skin sites

Widespread involvement

Schematic (not histology)

Slide 23 · Patch, plaque and tumor are not synonyms

Form

Gross appearance

Broad significance

Patch

Flat, scaly erythematous area

Often early presentation

Plaque

Raised, indurated scaling lesion

More established skin disease

Tumor

Fungating or nodular mass

Advanced cutaneous burden

Slide 24 · Clinical evolution is often slow

Progression between forms may occur over prolonged intervals.

Many patients remain localized to skin.

Late nodal or visceral dissemination is a distinct clinical change.

Long patch phase

Possible plaque development

Possible tumor/systemic phase

Time and progression are variable

Slide 25 · Skin-surface burden influences prognosis

Outcome to the percentage of body surface involved.

Extent of cutaneous involvement is not merely cosmetic severity.

This source does not provide numerical staging thresholds.

Limited skin burden

More extensive skin burden

Tumors or systemic involvement

Qualitative risk relationships — no numeric cut-offs implied

Slide 26 · Tumor nodules indicate greater risk

The appearance of tumor nodules correlates with systemic spread.

Nodular transformation reflects altered tissue growth behavior.

Tumor presence is associated with more aggressive disease.

Nodules appear

Deeper dermal growth

Higher-risk course

Schematic (not histology)

Slide 27 · Extracutaneous spread changes the interpretation

Overt spread to lymph nodes or viscera is usually a late event.

Presence of systemic disease is linked with a worse prognosis.

Circulating cells alone are not equivalent to overt organ infiltration.

Cutaneous disease

Overt nodal / visceral involvement

Higher disease burden

Schematic (not histology)

Slide 28 · Normal skin compartments orient the biopsy

Epidermis overlies the papillary and deeper dermis.

Mycosis fungoides combines superficial dermal infiltration with epidermal involvement.

Different clinical phases shift the depth and distribution of atypical cells.

Epidermis

Dermis

No neoplastic lymphocytes shown

Schematic (not histology)

Slide 29 · Superficial dermal band of atypical cells

A band-like population of atypical lymphocytes collects in superficial dermis.

This localization is a characteristic morphologic clue.

Band-like distribution must be assessed along with epidermotropism.

Epidermis

Dermis

Schematic (not histology)

Slide 30 · Epidermotropism: Lymphocytes enter epidermis

Atypical T cells infiltrate epidermis as individual cells.

The finding distinguishes epidermal infiltration from a purely dermal band.

Epidermotropism is prominent in many patch and plaque lesions.

Epidermis

Dermis

Schematic (not histology)

Slide 31 · Pautrier microabscesses are intraepidermal clusters

Small groups of atypical lymphocytes can collect within the epidermis.

These clusters are termed Pautrier microabscesses.

They are lymphoid collections, not neutrophilic abscesses.

Epidermis

Dermis

Cluster

Schematic (not histology)

Slide 32 · Nuclear folding produces cerebriform contours

Atypical lymphocytes may show markedly infolded nuclear membranes.

The resulting outline appears convoluted or cerebriform.

Nuclear contour complements, rather than replaces, assessment of architecture.

Convoluted nuclear outline

Schematic (not histology)

Slide 33 · Patch-stage histology may be subtle

The infiltrate may be superficial and limited in density.

Epidermotropism can be present despite a clinically understated lesion.

An inflammatory-appearing specimen does not automatically exclude MF.

Epidermis

Dermis

Schematic (not histology)

Slide 34 · Plaque-stage histology emphasizes epidermotropism

Plaques frequently contain conspicuous epidermal atypical lymphocytes.

An expanded superficial dermal infiltrate may coexist.

Pautrier microabscesses can be seen in this setting.

Epidermis

Dermis

Schematic (not histology)

Slide 35 · Tumor-stage histology becomes deeply dermal

Malignant lymphocytes grow more extensively within dermis.

The deep infiltrate produces clinically appreciable nodules.

Tumor lesions may show less epidermotropism than earlier patches.

Epidermis

Dermis

Dense deeper growth

Schematic (not histology)

Slide 36 · Epidermotropism can diminish as tumors develop

Patch/plaque disease typically involves the epidermis prominently.

Advanced tumor-stage cells can grow deeply and lose epidermotropism.

An absent epidermotropic pattern does not exclude advanced MF.

Patch / plaque

Epidermal infiltration conspicuous

Tumor

Deeper growth; Often reduced epidermotropism

Slide 37 · A single biopsy field is not the whole diagnosis

Assess

Question

Why it matters

Distribution

Where are cells concentrated?

Superficial vs deep

Epidermis

Single cells or clusters?

Epidermotropism

Nuclei

Convoluted contours?

Cytologic support

Clinical form

Patch, plaque or nodule?

Stage correlation

Slide 38 · Morphology and clinical phase are linked

Clinical form

Dominant microscopic emphasis

Visible correlate

Patch

Superficial sparse infiltrate; epidermotropism

Flat scaly lesion

Plaque

Dermal band and epidermal atypical cells

Thickened scaling plaque

Tumor

Dense deeper dermal infiltrate

Nodular mass

Slide 39 · Diagnosis integrates several lines of evidence

A compatible lesion history prompts a representative skin biopsy.

Morphology establishes the distribution of atypical lymphocytes.

T-cell phenotype and clonality can provide corroboration.

Clinical pattern

Biopsy architecture

T-cell studies

Integrated judgment

Schematic (not histology)

Slide 40 · The T-cell phenotype is supportive

MF is most often associated with a CD4+ helper T-cell population.

Surface T-cell antigens may be aberrantly combined.

Phenotype must be interpreted with morphology and clinical presentation.

Expected lineage

CD4+ helper T cell

Possible aberrancy

Unusual T-cell antigen combinations

Slide 41 · Clonality is evidence, not a complete diagnosis

T-cell receptor rearrangements can demonstrate a shared clone.

A molecular result does not reveal lesion architecture or clinical course.

The final diagnosis is clinicopathologic, not a single-assay label.

Molecular information

Presence of a T-cell clone

Clinical/pathologic information

Whether findings fit MF

Slide 42 · Early MF requires careful differential diagnosis

Consideration

Shared appearance

Useful distinction

Eczema-like dermatitis

Erythematous scaly patch

Persistence + atypical epidermotropic cells

Psoriasis

Scaling plaque

Lymphoid infiltrate architecture

Other CTCL

Cutaneous T-cell lesion

Entity-specific clinical presentation

Slide 43 · Eczema-like lesions are not always eczema

MF may initially present as an inflammatory-appearing patch.

Discordance between persistent lesions and a nonspecific label deserves review.

The biopsy should be correlated with the lesion selected for sampling.

Clinical mimic

Chronic eczematous patch

Pathologic concern

Atypical lymphocytes in epidermis

Slide 44 · Psoriasis-like plaques require tissue correlation

Scale and erythema occur in both disorders.

Raised plaque morphology alone does not establish a neoplasm.

In MF, lymphoid epidermotropism and cytologic atypia are key clues.

Psoriasiform surface

Scale and thickening

MF-specific concern

Atypical epidermotropic T-cell infiltrate

Slide 45 · Repeated evaluation may be necessary in subtle cases

Early patch-stage histology may be difficult to classify conclusively.

Review of persistent lesions and additional biopsies can be necessary.

An equivocal sample should not be forced into a definitive diagnosis.

Persistent atypical rash

Clinicopathologic review

Repeat sampling if justified

Time and progression are variable

Slide 46 · Recognize a diagnostic pitfall in tumor disease

Tumor-stage lesions can lose classic epidermotropism.

Relying only on epidermal infiltrates risks overlooking advanced disease.

Clinical evolution and dermal lymphoid morphology remain relevant.

Epidermis

Dermis

Dense deeper growth

Schematic (not histology)

Slide 47 · Sézary syndrome: A related but distinct entity

Both diseases involve skin-homing CD4+ T-cell neoplasms.

Sézary syndrome has generalized erythroderma, blood involvement and nodes.

The clinical courses and patterns of tumefaction differ.

Mycosis fungoides

Patches, plaques, possible tumors

Sézary syndrome

Erythroderma + blood + nodes

Slide 48 · Generalized erythroderma defines the skin picture in Sézary

Sézary syndrome typically manifests with diffuse exfoliative erythroderma.

This differs from the usual evolution of discrete MF lesions.

Generalized lymphadenopathy commonly accompanies it.

Erythroderma + lymphadenopathy

Slide 49 · Blood involvement distinguishes Sézary syndrome

Sézary syndrome includes leukemia of circulating neoplastic cells.

These cells characteristically display cerebriform nuclear contours.

Blood findings are interpreted together with skin and nodes.

Diffuse erythroderma

Sézary cells in blood

Generalized nodes

Schematic (not histology)

Slide 50 · Mycosis fungoides versus Sézary syndrome

Feature

Mycosis fungoides

Sézary syndrome

Skin

Patch → plaque → tumor

Diffuse exfoliative erythroderma

Blood

Sensitive tests may detect cells early

Overt leukemic involvement

Tumors

May develop

Skin tumefaction uncommon

Overall course

Often indolent

Typically more aggressive

Slide 51 · Early cell circulation does not equal overt systemic disease

Sensitive analyses can detect MF cells in blood, nodes or marrow early.

Clinically evident extracutaneous disease usually develops much later.

This distinction reconciles biological trafficking with cutaneous indolence.

Sensitive detection

Tumor cells may circulate

Overt dissemination

Usually a late clinical event

Slide 52 · Outcome in mycosis fungoides is variable

MF often progresses indolently with prolonged skin localization.

Chapter 13 reports a median survival of approximately 10 years.

Extent, tumor nodules and systemic involvement modify prognosis.

Limited skin burden

More extensive skin burden

Tumors or systemic involvement

Qualitative risk relationships — no numeric cut-offs implied

Slide 53 · Sézary syndrome generally has a worse course

Chapter 13 characterizes Sézary syndrome as more aggressive than MF.

It reports that only a minority remain alive five years after diagnosis.

Population-level statements cannot predict an individual patient.

MF

Often prolonged cutaneous course

Sézary

More aggressive systemic behavior

Slide 54 · Aggressive transformation can occur late

MF occasionally evolves into aggressive T-cell lymphoma.

This as a possible terminal event.

New aggressive clinical changes warrant reconsideration of disease biology.

Indolent MF

Occasional transformation

Aggressive T-cell lymphoma

Schematic (not histology)

Slide 55 · Skin-directed therapy targets early lesions

Localized patches and plaques are commonly managed with skin-directed measures.

Topical steroids and ultraviolet light.

The rationale is disease largely confined to cutaneous compartments.

Early skin disease

Local cutaneous therapy

Lesion control

Schematic (not histology)

Slide 56 · Topical corticosteroids: Early-lesion approach

Topical steroids as a treatment option for early MF.

The treatment acts at the site of visible disease.

The text does not specify regimens or response percentages.

Setting

Early skin lesions

Treatment modality

Topical steroid therapy

Slide 57 · Ultraviolet therapy is another skin-directed option

Ultraviolet light therapy is cited for early skin lesions.

Phototherapy is distinct from systemic cytotoxic chemotherapy.

Treatment choice must account for burden and stage.

Cutaneous lesions

Ultraviolet light exposure

Skin-directed management

Schematic (not histology)

Slide 58 · Advanced disease may require systemic treatment

Systemic chemotherapy for more aggressive disease.

Clinical tumor development or extracutaneous disease changes management.

Therapeutic details beyond this principle require specialist guidance.

Early skin disease

Topical / UV modalities

Advanced aggressive disease

Systemic treatment

Slide 59 · Follow-up focuses on meaningful change

Assess new plaque thickening, tumors, ulceration and broader skin involvement.

Look for evidence of clinically overt extracutaneous disease.

Clinical progression should trigger renewed clinicopathologic assessment.

Skin burden

Tumor emergence

Systemic features

Risk reassessment

Schematic (not histology)

Slide 60 · Case study: A persistent scaly patch

Hypothetical teaching case

A hypothetical patient aged 54 has a chronic red-brown, scaling truncal patch.

The lesion has been described as eczema-like but persists.

Question: Which tissue feature would most strengthen concern for MF?

Slide 61 · Case interpretation: Subtle clinical disease

Reasoning

Persistence and a truncal patch are compatible but not pathognomonic.

Biopsy can disclose atypical epidermotropic T cells.

Clonality and immunophenotype may support an integrated diagnosis.

Clinical suspicion → representative biopsy → integrated interpretation.

Slide 62 · Case study: Progression to a nodule

Hypothetical teaching case

A patient with long-standing scaling plaques develops a fungating nodule.

The tumor contains a dense population of atypical cells deep in the dermis.

Question: Must prominent epidermotropism still be present?

Slide 63 · Case interpretation: A changed tissue pattern

Reasoning

Nodule formation corresponds to greater dermal tumor burden.

Epidermotropism may diminish in advanced nodular lesions.

New tumors also alter assessment of prognosis and systemic spread.

Deep dermal growth can dominate tumor-stage disease.

Slide 64 · Morphology challenge: Identify the pattern

Superficial dermal band plus intraepidermal atypical cells:

What is the name for individual-cell epidermal migration?

What is the name for small intraepidermal clusters?

Epidermis

Dermis

Cluster

Schematic (not histology)

Slide 65 · Morphology challenge: Terms and interpretation

Observation

Term

Interpretation

Atypical cells within epidermis

Epidermotropism

Neoplastic cells cross tissue boundary

Small intraepidermal clusters

Pautrier microabscesses

Focal lymphoid aggregates

Convoluted lymphoid nuclei

Cerebriform contour

Atypical cell morphology

Slide 66 · Integrating the disease in one mechanism

Clonal, skin-homing CD4+ T cells underlie the lymphoma.

Superficial dermal and epidermal infiltration produces early lesions.

Progressive dermal growth and eventual spread explain advanced disease.

Skin-homing T-cell clone

Epidermotropism

Patch / plaque

Tumor ± dissemination

Schematic (not histology)

Slide 67 · High-yield discriminators

If you see…

Think about…

Do not forget…

Scaly chronic truncal patches

Possible early MF

Inflammatory mimics

Superficial band + epidermotropism

Characteristic MF morphology

Clinical correlation

Deep dermal tumor; little epidermotropism

Advanced tumor-stage MF

Epidermotropism can wane

Erythroderma + blood disease + nodes

Sézary syndrome

Different clinical entity

Slide 68 · Core teaching conclusions

MF is a skin-homing, usually CD4+ clonal T-cell lymphoma.

Clinical lesions classically evolve through patch, plaque and tumor patterns.

Band-like dermal infiltrates, epidermotropism and Pautrier clusters are key clues.

Tumor nodules and overt systemic spread indicate higher-risk disease.

Slide 69 · Source references

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. 2026. Chapter 25, pp. 1044–1046.

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. 2026. Chapter 13, pp. 551–552.

DermNet. Mycosis fungoides pathology (supplementary diagnostic context). https://dermnetnz.org/topics/mycosis-fungoides-pathology