Cervical Squamous Intraepithelial Lesions

Slide 1 · Cervical Squamous

Intraepithelial Lesions

HPV pathogenesis · morphology · classification · natural history

A pathology teaching lecture

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

Relate HPV biology to LSIL and HSIL morphology

Translate dysplasia/CIN terminology into two-tier SIL categories

Use epithelial maturation, koilocytic change, p16 and Ki-67 in lesion interpretation

Interpret Robbins natural-history estimates and clinical implications

Slide 3 · Why SIL matters

A cervical squamous intraepithelial lesion is an epithelial abnormality associated with HPV infection

Some lesions are precursors of invasive squamous carcinoma

The long interval before many invasive cancers creates an opportunity for detection

Grade informs the distinction between surveillance-oriented and treatment-oriented pathways

Slide 4 · Cervical tissue compartments

SCHEMATIC — epithelial transition, not a histologic specimen

Stratified squamous

Columnar epithelium

The squamocolumnar junction is a transition between epithelial phenotypes

Slide 5 · The transformation zone creates vulnerability

Immature

Basal cells

HPV

Entry

Productive

Infection

SIL

Changes

HPV requires access to immature basal epithelial cells

Mature, intact squamous surfaces ordinarily resist productive entry

Repair and immature squamous metaplasia expose susceptible epithelial populations

Cervical transformation-zone biology helps explain lesion predilection

Slide 6 · A lesion is not equivalent to invasive cancer

Intraepithelial

Atypical cells within epithelial compartment

Architectural and nuclear change assessed above stroma

Invasive

Malignant epithelium penetrates the underlying stroma

A separate entity beyond the SIL classification

Invasive carcinoma is a distinct diagnostic endpoint

Slide 7 · Three successive classification vocabularies

Historical dysplasia

CIN system

Two-tier SIL

Mild

CIN 1

LSIL

Moderate

CIN 2

HSIL

Severe / carcinoma in situ

CIN 3

HSIL

Older vocabulary: Mild, moderate, and severe dysplasia; Carcinoma in situ

Slide 8 · LSIL maps to CIN 1

CIN 1 / LSIL

Surface

Stromal side

Editable schematic — not histology

LSIL corresponds to mild dysplasia / CIN 1

Immature atypical cells largely occupy the lower epithelial third

Maturation is retained in the upper epithelial layers

Koilocytic changes commonly signal productive HPV replication

Slide 9 · HSIL unifies CIN 2 and CIN 3

Normal

Surface

Stromal side

Editable schematic — not histology

HSIL includes CIN 2 and CIN 3 in the two-tier terminology

Abnormal proliferating immature cells expand beyond the lower third

CIN 3 may show nearly full-thickness loss of maturation

The higher-grade category is clinically important because progression risk is greater

Slide 10 · Why two-tier terminology is useful

LSIL

Usually transient productive infection

Common spontaneous regression

HSIL

Deregulated cell growth

Greater concern for malignant progression

Management still requires case-specific clinical evaluation

Slide 11 · HPV is central to cervical squamous neoplasia

Human papillomaviruses are DNA viruses classified by oncogenic risk

High-risk types are central to cervical precursor lesions and carcinoma

Many genital HPV infections are asymptomatic

Viral presence alone is not equivalent to a histologic SIL

Slide 12 · High-risk and low-risk are biologic groups

High-risk HPV

E6/E7 strongly impair tumour suppressor control

Associated with cervical precursors and cancer

Low-risk HPV

Different E6/E7 interactions

Commonly causes condylomata

Risk designation concerns oncogenic potential, not whether infection is symptomatic

Slide 13 · HPV-16 is prominent

HPV-16 as the most common type in LSIL and HSIL

The text reports high-risk HPV association in >80% of LSIL and 100% of HSIL

These figures summarize the textbook source rather than a universal individual test rule

HPV type alone cannot determine a lesion’s outcome

Slide 14 · HPV infection is common; Persistence is selective

HPV

Exposure

Transient

Infection

Clearance

(common)

Persistence

(risk)

The source reports clearance of ~50% of infections within 8 months

Approximately 90% clear within 2 years

High-risk infections persist longer on average than low-risk infections

Persistence increases the chance of precursor lesions and carcinoma

Slide 15 · Basal-cell infection precedes surface changes

Normal

Surface

Stromal side

Editable schematic — not histology

Entry occurs in immature basal epithelial cells

Virus replication is amplified in differentiating cells above the basal layer

The infected epithelium becomes abnormal in a stratified, layer-dependent fashion

These differences produce diagnostic histologic and biomarker patterns

Slide 16 · Productive infection: A layered viral life cycle

Basal

Infection

Upward

Differentiation

HPV DNA

Replication

Surface

Koilocytes

Basal cells maintain an infected population

Maturing keratinocytes support substantial HPV DNA replication

Superficial koilocytes can contain particularly abundant viral DNA

Superficial proliferative activity is abnormal for normal squamous epithelium

Slide 17 · E6 and E7 help force cell-cycle progression

High-risk

HPV

E6 → p53

Dysfunction

E7 → RB

Dysfunction

Cell-cycle

Deregulation

High-risk HPV E7 interferes with the RB pathway

High-risk HPV E6 promotes loss of p53 function

The combined effect favors cell cycling despite maturation cues

Impaired growth control facilitates additional genetic alterations

Slide 18 · E7 disrupts the RB checkpoint

E7

Expression

RB / p21 / p27

Restraint reduced

Cell-cycle

Progression

Aberrant

Proliferation

Proteasomal degradation of RB by E7

E7 also interferes with the cell-cycle inhibitors p21 and p27

Reduced checkpoint restraint promotes continued cell-cycle transit

The consequences are important in differentiated epithelial layers

Slide 19 · E6 weakens p53 surveillance

E6

Expression

P53

Degradation

DNA damage

Response reduced

Increased

Cell survival

High-risk HPV E6 promotes proteasome-mediated p53 degradation

P53 loss weakens the response to DNA injury

E6 can up-regulate telomerase, favoring replicative persistence

These changes contribute to cellular immortalization and progression potential

Slide 20 · E5 contributes to koilocytic morphology

SCHEMATIC — koilocyte features, not a clinical specimen

Perinuclear halo

Enlarged atypical nucleus

The visible nuclear changes plus halo constitute koilocytic atypia

Slide 21 · Episomal and integrated HPV are not synonymous

Episomal pattern

Common in precursor lesions

Supports productive viral genome maintenance

Integrated pattern

Frequent in established carcinomas

May further deregulate E6/E7 expression

This contrast is a general pathogenetic association, not a stand-alone SIL grading test

Slide 22 · Why infection does not always progress

Most infections resolve rather than become persistent

The host immune response influences viral clearance

Co-carcinogenic exposures and host factors modify progression risk

A molecular risk genotype cannot predict a specific patient’s clinical course

Slide 23 · LSIL: Productive viral infection dominates

CIN 1 / LSIL

Surface

Stromal side

Editable schematic — not histology

High epithelial viral replication is a defining biologic theme

Host growth regulation is disturbed, but maturation remains evident

Koilocytes are characteristic cytopathic correlates

Spontaneous regression is more common than malignant progression

Slide 24 · HSIL: Cellular deregulation dominates

Normal

Surface

Stromal side

Editable schematic — not histology

Expansion of proliferating immature squamous cells is prominent

Epithelial maturation is markedly reduced or arrested

Viral replication is lower than in productive LSIL

Cell-cycle derangement may become irreversible

Slide 25 · The normal squamous baseline

Normal

Surface

Stromal side

Editable schematic — not histology

Basal immature cells ordinarily form a thin proliferative compartment

Maturation increases toward the epithelial surface

Nuclei become less conspicuous in upper layers

Comparing altered tissue to this baseline is essential

Slide 26 · The grading principle is vertical extent

Normal

CIN 1 / LSIL

CIN 2 / HSIL

CIN 3 / HSIL

Assess how far immature atypical cells extend above the basal layer

Schematic epithelial compartments — not a histologic specimen

Slide 27 · Nuclear enlargement signals atypia

SCHEMATIC — koilocyte features, not a clinical specimen

Perinuclear halo

Enlarged atypical nucleus

Architecture and cytology should be read together

Slide 28 · Hyperchromasia and coarse chromatin

Hyperchromasia denotes unusually dark-staining nuclei

Coarse nuclear chromatin is part of Robbins’ diagnostic description

These features accompany irregular proliferation and differentiation

Neither feature by itself determines LSIL versus HSIL

Slide 29 · Variation in nuclear size and shape

Nuclear pleomorphism occurs within abnormal squamous epithelium

Assess variability across cells, not just one atypical nucleus

Anatomic location of atypical cells changes the grade interpretation

Koilocytic change provides an HPV-associated cytopathic context

Slide 30 · Koilocytosis combines two findings

SCHEMATIC — koilocyte features, not a clinical specimen

Perinuclear halo

Enlarged atypical nucleus

Koilocytosis is a morphologic sign of productive HPV effect

Slide 31 · LSIL: Maturation is retained

CIN 1 / LSIL

Surface

Stromal side

Editable schematic — not histology

The abnormal immature compartment is limited mainly to the lower third

Superficial squamous differentiation remains visible

Koilocytic atypia may be apparent in maturing upper cells

This architecture aligns with an active productive infection

Slide 32 · CIN 2: Atypia rises into intermediate layers

CIN 2 / HSIL

Surface

Stromal side

Editable schematic — not histology

Atypical immature cells extend above the epithelial lower third

Surface maturation is reduced relative to LSIL

This pattern falls within HSIL under the two-tier system

The CIN 2 designation expresses its location within a continuum

Slide 33 · CIN 3: Maturation may be lost throughout

CIN 3 / HSIL

Surface

Stromal side

Editable schematic — not histology

Immature atypical cells extend to the epithelial surface

Atypia is diffuse across much or all of epithelial thickness

The architecture corresponds to severe dysplasia / carcinoma in situ

CIN 3 is still an intraepithelial lesion unless stromal invasion is demonstrated

Slide 34 · Read the full epithelial column

Normal

CIN 1 / LSIL

CIN 2 / HSIL

CIN 3 / HSIL

Locate the basement-membrane side and the luminal surface

Schematic epithelial compartments — not a histologic specimen

Slide 35 · Do not confuse grade with invasion

Grade

Degree of epithelial maturation loss

Distribution of atypical cells

Invasion

Relation to epithelial–stromal boundary

Presence of malignant cells in stroma

A complete tissue assessment is needed when invasion is suspected

Slide 36 · Atypia must be assessed in context

Inflammation and repair can cause atypical-appearing squamous cells

Marked cervicitis can disturb Pap cytology

Cytology abnormalities require appropriate diagnostic correlation

Avoid equating isolated nuclear atypia with tissue-confirmed HSIL

Slide 37 · Morphologic spectrum: A single visual framework

Normal

CIN 1 / LSIL

CIN 2 / HSIL

CIN 3 / HSIL

Normal epithelium maintains an organized maturation gradient

Schematic epithelial compartments — not a histologic specimen

Slide 38 · Ki-67 is a marker of proliferative activity

SCHEMATIC — vertical staining distributions; Not clinical immunohistochemistry

Normal proliferation

Upward Ki-67

P16 overexpression

Normal squamous epithelium restricts proliferation largely to basal cells

HPV-related lesions show Ki-67-positive cells higher in the epithelium

Slide 39 · P16 reflects disturbed cell-cycle control

SCHEMATIC — vertical staining distributions; Not clinical immunohistochemistry

Normal proliferation

Upward Ki-67

P16 overexpression

P16 is a cyclin-dependent kinase inhibitor

Its overexpression in high-risk HPV-associated SIL

Slide 40 · P16 and Ki-67 answer different questions

Test

Question answered

Interpretive caution

H&E

What is the tissue architecture and atypia?

Primary morphologic assessment

Ki-67 IHC

Where are cycling cells located?

Evaluate vertical distribution

p16 IHC

Is the cell-cycle response altered?

Interpret pattern and H&E together

HPV DNA assay

Is viral DNA detected?

Detection is not synonymous with HSIL

Ki-67 reflects where cells are actively cycling

Slide 41 · HPV DNA localizes to maturing keratinocytes

SCHEMATIC — viral DNA and Ki-67 localize to different epithelial compartments

HPV DNA: Mature upper cells

Ki-67: Aberrant upward cycling

Viral replication predominantly above

Proliferation extends beyond basal layer

Robbins Fig. 22.15 describes abundant HPV DNA in superficial koilocytes

In situ hybridization demonstrates viral DNA within the tissue

Slide 42 · Diagnostic layers must be integrated

H&E

Architecture

Nuclear

Atypia

Adjunct

Markers

Integrated

Grade

Begin with full-thickness H&E assessment

Interpret koilocytosis and the position of atypical immature cells

Use p16 and Ki-67 when the histology is equivocal

Correlate molecular/cytologic information without conflating assay types

Slide 43 · Pap cytology reflects exfoliated surface cells

Pap test

Exfoliated-cell nuclear/cytoplasmic features

Screening and detection context

Biopsy

Entire epithelium and stromal interface

Histologic grading context

Biopsy supplies tissue architecture for histologic grading

Slide 44 · Screening identifies, tissue assessment classifies

Screening

Result

Colposcopic

Evaluation

Directed

Biopsy

Histologic

Classification

A Pap smear can detect squamous precursor abnormalities

High-risk HPV testing detects viral nucleic acid

Colposcopy localizes suspicious cervical areas for biopsy

The definitive morphologic interpretation depends on tissue when sampled

Slide 45 · HPV testing and cytology are not interchangeable

Dimension

Cervical cytology

High-risk HPV test

Analyte

Exfoliated-cell morphology

Viral nucleic acid

Robbins comparison

Lower sensitivity; higher specificity

Higher sensitivity; lower specificity

Positive result

Cellular change detected

Virus detected

Histologic grade?

No

No

HPV DNA testing is more sensitive and less specific than the Pap test in the Robbins comparison

Slide 46 · Colposcopy and biopsy connect tests to tissue

Acetic acid highlighting abnormal epithelium

Colposcopy aids site selection for biopsy

Tissue shows the distribution of immature atypical cells

The biopsy is interpreted in the clinical and screening context

Slide 47 · LSIL is substantially more common than HSIL

LSIL is approximately tenfold more common than HSIL

This reflects the common productive infection pathway

Prevalence alone should not be used to classify an individual biopsy

The contrast in frequency must be considered with different progression risks

Slide 48 · LSIL natural history: Approximate source values

Regress

60%

Persist

30%

Progress to HSIL

10%

Source: Robbins Table 22.1 — approximate estimates

These are aggregated estimates rather than individualized probabilities

Slide 49 · HSIL natural history: Approximate source values

Regress

30%

Persist

60%

Progress to carcinoma

10%

Source: Robbins Table 22.1 — approximate estimates

The data do not justify predicting a single patient’s outcome

Slide 50 · The time frame changes interpretation

Statement

Time qualifier

Interpretive point

SIL fate table

Approx. 2-year follow-up

Regression/persistence estimates

HSIL → carcinoma

2–10 years (table note)

Progression fraction uses different window

Invasive evolution

Often decades overall

Long precursor phase

The table heading describes an approximate 2-year follow-up

Slide 51 · Most LSIL does not evolve into HSIL

Regression is the predominant course reported for LSIL

LSIL often represents a productive, self-limited viral infection

The malignancy-prevention concern is greatest when high-grade disease develops

Follow-up decisions must be individualized beyond a textbook percentage

Slide 52 · Not every HSIL has a recognized LSIL precursor

Recognized

LSIL

Progression

To HSIL

Or de novo

HSIL

High-grade

Precursor

Most HSIL develops from LSIL

About 20% of HSIL is reported to arise de novo

This challenges the idea that every case follows a documented stepwise sequence

Absence of known prior LSIL does not exclude HSIL

Slide 53 · Risk varies beyond viral genotype

HPV-16 infection is associated with greater progression risk

Immune factors can influence persistence or clearance

Co-carcinogenic influences also modify risk

One HPV result cannot forecast a defined histologic outcome

Slide 54 · Clinical implications differ by grade

LSIL

Spontaneous regression frequent

Conservative follow-up often appropriate

HSIL

Greater progression concern

Treatment commonly considered

Histologic findings should be interpreted alongside the clinical scenario

Slide 55 · Prevention begins before morphologic HSIL

HPV vaccination targets relevant viral genotypes

Prevention and screening interrupt the pathway to invasive cancer

Robbins stresses continuation of screening despite vaccination

Recommendations depend on updated jurisdictional guidance

Slide 56 · Why screening is effective for cervical lesions

Long precursor

Interval

Detectable

Cellular changes

Biopsy /

Classification

Prevention of

Invasion

Precursor lesions can shed abnormal cells before invasion

The cervix is accessible to cytology, HPV testing, and colposcopy

Progression is often sufficiently prolonged for detection

These factors underpin the success of cervical cancer prevention

Slide 57 · Case 1: Koilocytosis with surface maturation

Clinicopathologic reasoning

Biopsy shows atypia concentrated in the lower epithelial third

Upper squamous layers mature; Cells show perinuclear halos with abnormal nuclei

Question: Which SIL grade is most compatible with this pattern?

What underlying viral program does the architecture suggest?

Slide 58 · Case 1 interpretation: Productive LSIL

CIN 1 / LSIL

Surface

Stromal side

Editable schematic — not histology

CIN 1 / LSIL best fits lower-third atypia with maturation

Koilocytic nuclear changes support a cytopathic HPV effect

Productive replication is greatest in differentiating upper cells

Many such lesions regress; Severity is not determined by HPV detection alone

Slide 59 · Case 2: Widespread immature cells

Clinicopathologic reasoning

Biopsy shows atypical nuclei extending toward the surface

There is little residual epithelial maturation

Question: Which SIL category is appropriate?

What additional relationship must be assessed before diagnosing invasion?

Slide 60 · Case 2 interpretation: HSIL, not necessarily invasion

CIN 3 / HSIL

Surface

Stromal side

Editable schematic — not histology

Diffuse atypia and maturation loss support HSIL / CIN 3

Full epithelial thickness does not establish stromal invasion

Confirm the epithelial–stromal relationship in the tissue sample

Proliferation and altered p16 patterns may offer supportive evidence

Slide 61 · Case 3: A positive HPV test without tissue atypia

Clinicopathologic reasoning

A screening sample is positive for a high-risk HPV genotype

No biopsy-confirmed SIL has been demonstrated

Question: Can HSIL be inferred directly from the viral test?

What additional information would establish a tissue diagnosis?

Slide 62 · Case 3 interpretation: Viral detection ≠ HSIL

Information

What it establishes

HPV DNA positive

Viral nucleic acid detected

Abnormal Pap

Cytomorphologic change detected

Biopsy with architecture

Histologic SIL grade can be assigned

HPV positivity indicates viral DNA detection, not histologic grading

Slide 63 · Case 4: Interpreting biomarkers

Clinicopathologic reasoning

A cervical biopsy has equivocal nuclear atypia

Ki-67 labeling is increased well above the basal layer

P16 expression is increased

Question: How should these findings be used in the final interpretation?

Slide 64 · Case 4 interpretation: Biomarkers are adjuncts

SCHEMATIC — vertical staining distributions; Not clinical immunohistochemistry

Normal proliferation

Upward Ki-67

P16 overexpression

Ki-67 demonstrates altered proliferative distribution

P16 supports an HPV-associated cell-cycle response

Slide 65 · Integrated LSIL–HSIL comparison

Feature

LSIL / CIN 1

HSIL / CIN 2–3

Immature atypical cells

Predominantly lower third

Extend beyond lower third

Surface maturation

Substantially retained

Reduced or lost

HPV replication

High/productive

Relatively lower

Typical course

Frequent regression

Higher progression risk

Atypia thickness, maturity, viral replication and behavior are linked

Slide 66 · Common interpretive errors to avoid

Do not call an isolated perinuclear halo koilocytosis without nuclear atypia

Do not equate positive HPV DNA with histologic HSIL

Do not call full-thickness dysplasia invasive carcinoma without stromal invasion

Do not read the natural-history estimates as individual prognoses

Slide 67 · Five ideas to retain

CIN 1 maps to LSIL; CIN 2 and CIN 3 map to HSIL

Extent of immature atypical cells and maturation is the grading backbone

Koilocytosis reflects productive HPV cytopathic effects

P16 and Ki-67 provide context to H&E morphology

Persistence, genotype and host factors influence risk, but outcomes vary

Slide 68 · Core references and source boundaries

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. Chapter 22, pp. 905–910

Primary SIL section: pp. 906–907; Fig. 22.14 and morphology text

Adjacent context: HPV pathogenesis, Fig. 22.15, Table 22.1, screening overview

Native epithelial drawings are schematic; authentic slide images not reproduced