Metaplasia Dysplasia and Carcinoma In Situ

Slide 1 · Metaplasia, Dysplasia, and

Carcinoma In Situ

Epithelial adaptation, precancer, and the invasion boundary

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Explain why chronic injury may replace an epithelial phenotype.

Identify cytologic and architectural criteria for dysplasia.

Diagnose the in situ–invasive boundary from epithelial architecture.

Interpret progression, regression, and precursor risk without assuming inevitability.

Slide 3 · Three related terms, three different meanings

Metaplasia

Replacement by another mature cell phenotype

Adaptation

Dysplasia

Disordered epithelial growth and maturation

Premalignant change

Carcinoma in situ

Full-thickness malignant cytology; No stromal invasion

Intraepithelial cancer

Slide 4 · Epithelial topography controls interpretation

Surface epithelium is separated from supporting stroma by a basement membrane.

Cytologic atypia describes the cells; Invasion describes their location.

The basement membrane is the critical boundary when distinguishing in situ from invasive carcinoma.

Simplified epithelial schematic

Stroma

Slide 5 · Normal stratified squamous epithelium matures upward

Proliferative basal cells are relatively tall and immature.

Progressive maturation produces flattened superficial squamous cells.

Orderly stratification provides the reference against which dysplasia is recognized.

Simplified epithelial schematic

Stroma

Slide 6 · Normal squamous mitoses are basally restricted

Normal mitotic activity is concentrated in the basal compartment.

Cells acquire differentiated morphology toward the epithelial surface.

Mitotic figures well above the basal region suggest disrupted maturation when accompanied by atypia.

Simplified epithelial schematic

Stroma

Slide 7 · Differentiation means resemblance to normal tissue

Differentiated phenotype

Loss of differentiation

Recognizable cell form

Specialized epithelial function

Orderly architectural organization

Failure of normal maturation

Architectural disarray

Potentially increasing atypia

Slide 8 · Metaplasia is replacement, not simply proliferation

One differentiated epithelial cell type is replaced by another.

Metaplasia usually occurs during tissue damage, repair, and regeneration.

It is generally an adaptive response to persistent adverse exposure.

Columnar

Stroma

Squamous

Stroma

Slide 9 · Metaplastic epithelium may tolerate the stress better

Chronic environmental stress

Repair / regeneration

Alternative, better-tolerated cell type

A more durable epithelial phenotype can survive a hostile local environment.

An adaptive advantage under stress does not imply normal physiologic function.

Slide 10 · Metaplasia is potentially reversible

Inciting exposure

Metaplastic differentiation

Exposure removed → potential reversal

Metaplasia as a reversible differentiation change.

Persistence and duration of the underlying injury influence the tissue context.

Reversibility should not be confused with absence of cancer risk.

Slide 11 · Bronchial epithelium: Columnar-to-squamous replacement

Chronic tobacco smoke exposure damages glandular/ciliated bronchial epithelium.

Stratified squamous cells may replace the normal columnar lining.

This is a classic epithelial example of metaplasia.

Ciliated columnar

Stroma

Squamous

Stroma

Slide 12 · Ciliated bronchial cells are functionally specialized

The normal airway lining contributes mucus secretion and ciliary transport.

These mechanisms help protect the respiratory tract against infection.

Loss of a differentiated function is important even if metaplastic cells survive better.

Simplified epithelial schematic

Stroma

Slide 13 · Squamous metaplasia trades function for resistance

Adaptation gained

Function lost

Rugged stratified squamous lining

Better tolerance of chronic irritation

Continued epithelial coverage

Normal mucus secretion

Ciliary clearance

Part of airway defense against infection

Slide 14 · The smoking-associated epithelial response is not cancer

Squamous metaplasia describes a change in cell type, not autonomous invasion.

It is not equivalent to dysplasia or carcinoma.

Persistent carcinogenic influences may also create a setting for later malignant transformation.

Ciliated columnar

Stroma

Squamous

Stroma

Slide 15 · Vitamin A deficiency can induce squamous metaplasia

Altered retinoic-acid signaling

Altered differentiation program

Squamous metaplasia

Squamous metaplasia in respiratory epithelium and cornea with vitamin A deficiency.

The corneal consequence is particularly detrimental to vision.

Slide 16 · Duct obstruction is another setting for squamous change

Stone / pressure / irritation

Ductal epithelial injury

Squamous metaplasia

Excretory ducts of salivary glands, pancreas, and bile ducts are cited examples.

The usual secretory columnar epithelium may be replaced by squamous lining.

Slide 17 · Metaplasia can also convert squamous to columnar

Direction is not restricted to columnar → squamous.

The best-known reverse example is Barrett esophagus.

The final phenotype depends on the local injury and differentiation context.

Squamous

Stroma

Columnar

Stroma

Slide 18 · Barrett esophagus develops under reflux injury

Gastroesophageal reflux

Damage to esophageal squamous lining

Glandular/intestinal-type replacement

Gastric secretions injure the native squamous esophageal epithelium.

Glandular epithelium is better able to withstand the acid-exposed environment.

Slide 19 · Barrett: Adaptive phenotype but clinically relevant risk

Immediate response

Long-term concern

Replacement of injured squamous epithelium

Acid-tolerant glandular/intestinal-type phenotype

Metaplastic epithelium is not inherently dysplastic

Cancers in Barrett-associated fields are typically gland-forming adenocarcinomas

Slide 20 · Different epithelia give rise to different carcinomas

Bronchial squamous metaplasia

Squamous phenotype

Associated with squamous cell carcinoma development

Barrett esophagus

Glandular/intestinal phenotype

Typically associated with adenocarcinoma

Slide 21 · Epithelial and mesenchymal metaplasia are distinct

Epithelial

One epithelial phenotype replaces another

May occur in a carcinogenic injury field

Mesenchymal

Bone, cartilage, or adipose differentiation at an unusual site

Robbins does not link this category to increased cancer risk

Slide 22 · Myositis ossificans illustrates mesenchymal metaplasia

Intramuscular injury / hemorrhage

Ectopic osseous differentiation

Bone within muscle

Bone formation in muscle after intramuscular hemorrhage.

The change may reflect injury rather than an obvious protective adaptation.

It must not be presented as epithelial dysplasia.

Slide 23 · Not every metaplasia increases cancer risk

Epithelial metaplasia

Connective-tissue metaplasia

Frequently linked with persistent epithelial injury

Certain metaplastic fields may precede carcinoma

Cancer is not an inevitable outcome

Cartilage, bone, or fat in unexpected tissue

May follow local tissue injury

Not associated with elevated cancer risk

Slide 24 · Metaplasia does not require mature-cell conversion

Tissue damage signals

Stem-cell reprogramming or adjacent-cell colonization

Changed epithelial phenotype

Robbins explicitly rejects direct phenotypic conversion of an already differentiated cell as the usual explanation.

Alternative cell-population sources can create the new epithelium.

Slide 25 · Local stem cells can adopt a new differentiation program

Signals in microenvironment

Local stem / progenitor population

Alternative lineage-specific genes

Stem-cell reprogramming changes the differentiation output of renewing tissue.

New epithelial cells acquire a phenotype suited to the exposed site.

Slide 26 · Adjacent differentiated populations can colonize tissue

Injured epithelial compartment

Colonization by cells from adjacent site

Alternative mature cell population

Colonization from a neighboring epithelial population as another mechanism.

This is distinct from reprogramming of local tissue stem cells.

Slide 27 · The microenvironment directs metaplastic differentiation

Cytokines / growth factors / extracellular matrix

Differentiation signaling

New tissue phenotype

Regenerative signals arise in the cells’ local environment.

They influence expression of genes driving a particular differentiation pathway.

Slide 28 · Retinoic acid links signaling to lineage identity

Retinoic acid

Nuclear retinoid receptors

Transcriptional differentiation program

Retinoic acid directly regulates transcription through nuclear retinoid receptors.

Deficiency or excess can disturb normal epithelial differentiation.

Slide 29 · Metaplasia differs fundamentally from hyperplasia

Hyperplasia

More cells from proliferation/renewal

Cell number changes

Metaplasia

Replacement with a different differentiated cell type

Cell phenotype changes

Dysplasia

Atypical growth and disordered maturation

Cell/architecture abnormality

Slide 30 · Metaplasia alone does not diagnose dysplasia

Metaplasia changes the epithelial phenotype.

Dysplasia requires atypical cytology and disturbed organization.

Dysplasia may arise within metaplastic epithelium, but the two changes are not synonymous.

Squamous

Stroma

Dysplasia

×

×

×

Stroma

× = mitosis

Slide 31 · Chronic injury creates a setting for precursor lesions

Chronic epithelial injury

Compensatory regeneration

At-risk epithelial field

Chronic inflammatory and precursor conditions can increase epithelial replication.

The presence of a precursor field raises cancer concern; It does not establish that invasive cancer is present.

Slide 32 · Precursor lesions are localized fields of risk

Hyperplasia

Increased epithelial proliferation

Metaplasia

Altered epithelial phenotype

Dysplasia

Cytologic atypia and architectural disarray

Robbins groups these morphologic changes among epithelial precursor lesions.

Slide 33 · Dysplasia literally means disordered growth

This premalignant morphologic change is encountered principally in epithelia.

Diagnosis relies on a combination of cellular and architectural abnormalities.

Unlike metaplasia, dysplasia denotes loss of growth and maturation order.

Simplified epithelial schematic

×

×

×

Stroma

× = mitosis

Slide 34 · Pleomorphism: Dysplastic cells vary in shape and size

Cell-to-cell uniformity is reduced.

Variation includes both cytoplasmic outlines and nuclear appearance.

Pleomorphism contributes to a dysplastic pattern but should be interpreted with architecture.

Simplified epithelial schematic

×

×

×

Stroma

× = mitosis

Slide 35 · Nuclear hyperchromasia is a dysplastic clue

Dysplastic cells often have large, deeply staining nuclei.

Hyperchromasia is assessed with other atypical cellular features.

Large dark nuclei alone do not establish basement-membrane invasion.

Simplified epithelial schematic

×

×

×

Stroma

× = mitosis

Slide 36 · A high nuclear-to-cytoplasmic ratio signals atypia

The nucleus occupies an increased share of the cell.

Elevated nuclear-to-cytoplasmic ratio among dysplastic features.

This finding complements nuclear pleomorphism and loss of maturation.

Simplified epithelial schematic

×

×

×

Stroma

× = mitosis

Slide 37 · Architectural disarray disrupts epithelial polarity

Normal relative cell positions and alignment are disturbed.

Epithelium loses the organized progression from basal cells to mature surface cells.

Architecture should be judged across a tissue section, not only in isolated cells.

Simplified epithelial schematic

×

×

×

Stroma

× = mitosis

Slide 38 · Failure of maturation is central to squamous dysplasia

Normal basal cells progressively become flatter toward the surface.

In dysplasia, immature basal-like cells may extend toward superficial levels.

The maturation defect may be partial or nearly complete.

Normal squamous

Stroma

Dysplasia

×

×

×

Stroma

× = mitosis

Slide 39 · Mitoses extend beyond the basal compartment

Normal squamous mitoses generally remain basal.

Dysplasia shows increased mitoses, sometimes throughout the epithelial thickness.

Distribution adds diagnostic information beyond the absolute number of mitotic figures.

Normal squamous

Stroma

Dysplasia

×

×

×

Stroma

× = mitosis

Slide 40 · Normal and dysplastic epithelium differ in two dimensions

Cytology

Architecture

Pleomorphism

Large hyperchromatic nuclei

High nuclear-to-cytoplasmic ratio

Loss of stratified maturation

Epithelial polarity disorder

Mitoses above basal layer

Slide 41 · Recognize dysplasia from a pattern of features

Cytologic atypia

Disordered maturation and mitoses

Dysplastic epithelial pattern

Do not equate atypical nuclear appearance with tissue invasion.

The histologic pattern includes both cell morphology and tissue architecture.

Slide 42 · Dysplasia spans a range of morphologic severity

Some dysplasias retain part of the normal epithelial maturation pattern.

The most extensive atypical transformation may involve the entire epithelial thickness.

The full-thickness noninvasive extreme as carcinoma in situ.

Dysplasia

×

×

×

Stroma

× = mitosis

In situ

×

×

×

Stroma

× = mitosis

Slide 43 · Carcinoma in situ involves full epithelial thickness

The entire epithelium is replaced by markedly atypical cells.

Normal squamous surface maturation is absent.

The basement membrane remains intact and no tumor lies in underlying stroma.

Simplified epithelial schematic

×

×

×

Stroma

× = mitosis

Slide 44 · “In situ” is an anatomic statement

Malignant cytologic features can exist while the lesion remains within epithelium.

Cytologic malignancy does not automatically mean stromal invasion.

The decisive boundary is basement-membrane penetration.

Simplified epithelial schematic

×

×

×

Stroma

× = mitosis

Slide 45 · Intact basement membrane separates in situ from invasion

Carcinoma in situ: Atypical cells are restricted to the epithelial compartment.

Invasive carcinoma: Neoplastic cells extend into the subjacent stromal compartment.

Recognition of invasion changes the pathologic category.

In situ

×

×

×

Stroma

× = mitosis

Invasive

×

×

×

Stroma

Slide 46 · Invasion means extension into surrounding tissue

Malignant cells infiltrate adjacent structures rather than remaining intraepithelial.

Invasiveness as a major discriminator of malignancy.

This is separate from the mere appearance of severe nuclear atypia.

Simplified epithelial schematic

×

×

×

Stroma

Slide 47 · The classic in situ morphology has no stromal tumor

Robbins Figure 7.9 describes epithelium entirely replaced by atypical dysplastic cells.

Normal squamous differentiation is lost and mitoses reach superficial levels.

The described basement membrane is intact and the subepithelial stroma is free of tumor.

Simplified epithelial schematic

×

×

×

Stroma

× = mitosis

Slide 48 · Carcinoma in situ is recognized across several organs

Skin

In situ epithelial carcinoma can occur

Uterine cervix

Severe dysplasia/in situ change may precede invasion

Urinary bladder

In situ epithelial carcinoma can occur

Breast

In situ carcinoma can occur

Slide 49 · The cervix exemplifies a recognized precursor sequence

Severe epithelial dysplasia

Carcinoma in situ

Possible subsequent invasive cancer

Severe dysplasia or carcinoma in situ frequently antedates invasive cervical cancer.

This relationship supports precursor recognition but is not a guarantee of progression in every lesion.

Slide 50 · Dysplasia can abut invasive carcinoma

Dysplastic epithelium is often found adjacent to invasive tumor foci.

The proximity supports a histologic precursor relationship.

The boundary of invasive growth must still be established separately.

Dysplasia

×

×

×

Stroma

× = mitosis

Invasive

×

×

×

Stroma

Slide 51 · Molecular abnormalities may precede severe morphology

Early dysplastic lesion

Cancer-associated genetic changes may already be present

Morphologic progression remains variable

Mutations associated with cancer can be present even in mild dysplasia.

A molecular alteration alone does not establish invasion or inevitable progression.

Slide 52 · Invasive cancer reflects cumulative genomic change

Accumulating mutations

Additional epigenetic changes

Fully malignant phenotype

The time required for progression likely reflects acquisition of a sufficient set of changes.

The textbook does not prescribe a fixed number or universal order of changes for these lesions.

Slide 53 · Dysplasia is a precursor, not a guaranteed cancer

Possible regression

Possible progression

Removal of an inciting cause

Reversal of some moderately severe dysplasia

Return toward more orderly epithelium

Persistent precancerous field

Further molecular evolution

Development of invasive cancer in a subset

Slide 54 · Some in situ lesions may persist for years

Carcinoma in situ

Prolonged noninvasive persistence is possible

Invasion may occur later

Latency does not make carcinoma in situ biologically trivial.

Substantial untreated progression risk while emphasizing variability in timing.

Slide 55 · Cancer risk and cancer diagnosis are different claims

Metaplasia

Adaptation; May occur in an at-risk field

Not automatically dysplasia

Dysplasia

Premalignant epithelial alteration

Not automatically carcinoma

Carcinoma in situ

Malignant cytology without stromal invasion

Not invasive carcinoma

Invasive carcinoma

Tumor enters adjacent stroma

Requires demonstration of invasion

Slide 56 · Anatomic progression is not a required linear sequence

Normal epithelium

Metaplasia in some injury settings

Dysplasia in a subset

In situ / invasive cancer in a subset

Metaplasia can occur without dysplasia.

Dysplasia may arise in, but need not always follow, metaplastic epithelium.

Both regression and long-term noninvasive persistence are recognized possibilities.

Slide 57 · Diagnostic reasoning begins with the epithelial phenotype

Different mature epithelial phenotype?

If yes: Consider metaplasia

Assess separately for cytologic/architectural dysplasia

Metaplastic differentiation and dysplastic atypia answer different questions.

A single biopsy can contain both changes.

Slide 58 · Diagnostic reasoning next tests the stromal boundary

Severe full-thickness atypia

Inspect basement membrane / underlying stroma

Intact: In situ | breach: Invasive

Do not infer stromal invasion from nuclear atypia alone.

Interpret the epithelial compartment and underlying tissue together.

Slide 59 · Case: Smoker with bronchial squamous lining

Clinical–pathologic vignette

A bronchial sample from a person with prolonged tobacco exposure shows stratified squamous epithelium replacing a previously ciliated columnar lining; There is no described atypia.

Question

What morphologic term best describes the epithelial replacement?

Interpretation: Squamous metaplasia; Replacement of phenotype does not by itself diagnose dysplasia.

Slide 60 · Case: Chronic reflux with columnar-lined esophagus

Clinical–pathologic vignette

A patient with long-standing reflux has columnar/intestinal-type epithelium replacing the usual esophageal squamous lining.

Question

Is the fundamental morphologic change dysplasia or metaplasia?

Interpretation: Metaplasia. Dysplasia requires additional cytologic and architectural abnormalities.

Slide 61 · Case: Disordered squamous maturation

Clinical–pathologic vignette

A squamous epithelial biopsy shows large hyperchromatic nuclei, pleomorphism, disturbed stratification, and mitotic figures well above the basal region.

Question

Which constellation supports a premalignant diagnosis?

Interpretation: Epithelial dysplasia, based on combined cytologic and architectural abnormalities.

Slide 62 · Case: Atypia reaches the surface but stroma is free

Clinical–pathologic vignette

Squamous epithelium is replaced throughout its thickness by atypical cells. The basement membrane is intact and the underlying stroma contains no tumor.

Question

What distinguishes this lesion from invasive carcinoma?

Interpretation: The lesion meets Robbins’ description of carcinoma in situ; No stromal invasion is present.

Slide 63 · Case: A microscopic focus lies beneath the epithelium

Clinical–pathologic vignette

An epithelial malignancy with full-thickness atypia has an additional focus of tumor cells infiltrating beneath a breached epithelial–stromal boundary.

Question

Which finding changes the interpretation?

Interpretation: Stromal infiltration establishes invasion, rather than an exclusively in situ process.

Slide 64 · Common error: Equating metaplasia with malignant change

Incorrect inference

Source-consistent interpretation

New epithelial phenotype automatically means dysplasia

All metaplasia inevitably progresses to cancer

Metaplasia is an adaptive replacement

Dysplasia requires disordered cytology/architecture

Outcomes depend on tissue and exposure

Slide 65 · Common error: Using nuclear atypia as proof of invasion

What cytology can show

What invasion requires

Pleomorphism

Hyperchromasia

Elevated nuclear-to-cytoplasmic ratio

Tumor beyond the epithelial compartment

Evidence of stromal infiltration

Assessment of basement-membrane boundary

Slide 66 · Compare the four epithelial states

Normal

Orderly maturation

Basement membrane intact

Metaplastic

Different mature cell phenotype

Basement membrane intact

Dysplastic

Atypia and disordered growth

No invasion implied

Carcinoma in situ

Full-thickness cytologic malignancy

Basement membrane intact

Invasive carcinoma

Neoplastic infiltration

Beyond basement membrane

Slide 67 · Integrative interpretation: Appearance, site, boundary

Identify epithelial phenotype

Evaluate cytologic + architectural atypia

Examine stromal interface

State morphology precisely

Use “metaplasia” for mature phenotype replacement.

Use “dysplasia” for disordered epithelial growth.

Use “in situ” or “invasive” only after evaluating the anatomic boundary.

Slide 68 · Five statements that should remain distinct

Metaplasia is generally reversible and may sacrifice specialized function.

Dysplasia is a morphologic premalignant change, not certain future cancer.

Carcinoma in situ has severe full-thickness epithelial atypia without stromal invasion.

Accumulating genetic/epigenetic alterations may explain progression over time.

The basement membrane is central to the in situ–invasive distinction.

Slide 69 · Primary source and section context

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. (2026).

Chapter 7, “Neoplasia”: Metaplasia, Dysplasia, and Carcinoma In Situ, p. 241.

Related context: Chapter 2 “Metaplasia,” p. 55; Chapter 7 “Local Invasion,” pp. 241–242.

Figures discussed from the supplied textual descriptions; original diagnostic images not reproduced.