HSIL: Morphology, Biomarkers, and Clinical Implications

Definition and Classification

Pathogenesis

• E6 oncoprotein: binds and mediates destruction of p53, plus upregulates telomerase
• E7 oncoprotein: binds and inactivates RB protein, displacing E2F transcription factors and driving cell cycle progression
• High-risk HPV types integrate into the host genome, disrupting the viral gene that normally suppresses E6/E7 expression - this integration also increases genomic instability
• HPV-16, -18, -31, -33, -35, -39, -45, -51, -52, -56, -58, -59, and -68 collectively account for ~90% of high-grade lesions and cancer

Morphology

Histology (Tissue Sections)

• LSIL (CIN I) shows dysplasia only in the lower 1/3 with prominent koilocytes (HPV cytopathic effect) in the upper layers
• HSIL shows no significant koilocytic change, reflecting suppressed viral replication with high proliferative activity instead

Cytology (Pap Test)

• Markedly reduced cytoplasm relative to nucleus
• High nuclear-to-cytoplasmic (N:C) ratio - the most characteristic feature
• Hyperchromatic, coarsely granular nuclei
• Nuclear membrane irregularity
• Cells smaller than LSIL cells, appearing in sheets or singly

Biomarkers

1. p16^INK4a (CDKN2A) - Most Important Biomarker

• Mechanism: Normally, p16 is a cell-cycle inhibitor that suppresses CDK4/6. In HPV-driven dysplasia, E7 inactivates RB, which in turn removes negative feedback on p16 - leading to strong diffuse p16 overexpression ("block positivity")
• Pattern in HSIL: Strong, diffuse nuclear and cytoplasmic staining throughout the full or near-full thickness of the epithelium
• Pattern in LSIL/reactive changes: Patchy, weak, or negative
• Clinical use:
  • Resolves interobserver disagreement in ambiguous CIN 2 diagnoses (CIN 2 is the least reproducible grade)
  • p16 IHC improves reproducibility of cervical histology interpretation (PMID 38527169, 2024)
  • Guides management of CIN 2 in young women - p16-negative CIN 2 may be managed conservatively; p16-positive CIN 2 is treated as HSIL
• Per Berek & Novak's Gynecology: p16INK4a staining is useful for managing histological HSIL, and p16 IHC correlates with CIN grade

2. Ki-67 (MKI67)

• A nuclear marker of cellular proliferation
• In HSIL, Ki-67 positive cells extend into the upper epithelial layers (above the lower 1/3), reflecting loss of differentiation
• In normal or reactive epithelium, Ki-67 is confined to the basal/parabasal layers
• CINtec PLUS test: Dual staining with p16 + Ki-67 on the same cell is used in cytology triage - a cell that is simultaneously p16(+)/Ki-67(+) is an abnormal cell in an unphysiological state, highly specific for CIN 2+
• A 2025 prospective study confirmed that p16, Ki-67, and MCM2 immunocytochemistry all improve detection of cervical lesions (PMID 40530144)

3. MCM2 (Mini-Chromosome Maintenance Protein 2)

• A DNA replication licensing factor; overexpressed when HPV drives cell cycle re-entry
• Extends further up the epithelium in HSIL compared to LSIL
• Proposed as a complementary proliferation marker alongside Ki-67

4. HPV Testing

• High-risk HPV DNA/mRNA testing is a central triage tool, not a histologic biomarker per se
• HPV-16/18 genotyping has the highest individual-type risk for CIN 3+
• HPV E6/E7 mRNA testing reflects active viral oncogene expression and is more specific than DNA testing for identifying transforming infections
• Sensitivity of HPV testing for HSIL is higher than Pap cytology alone; specificity is lower - Symptom to Diagnosis, p. 1657

5. Other Emerging Markers

Natural History

• ~20% of HSIL cases arise de novo (without preceding LSIL)
• HSIL demonstrates low levels of viral replication (unlike LSIL which has abundant viral shedding) - this reflects HPV integration and oncogenic transformation
• Risk factors for progression from HSIL to invasive carcinoma: cigarette smoking, HIV/immunocompromise

Clinical Implications

Symptoms

Screening and Detection

• Pap test sensitivity for HSIL: ~56% (individual test); specificity ~97%
• HPV testing is more sensitive but less specific
• Co-testing (Pap + HPV) every 5 years (ages 30-65) or Pap alone every 3 years are preferred screening strategies
• Women with HSIL cytology must undergo colposcopy and directed biopsy - Berek & Novak's Gynecology, Key Point 9

Colposcopy Findings

Management

Post-treatment Surveillance

Summary Table

HSIL - Quick Reference

Morphology

• Dysplastic immature squamous cells extending >2/3 of epithelial thickness (CIN 2) or full thickness (CIN 3)
• Atypical mitoses above basal layer
• No koilocytic change (unlike LSIL)
• Disorderly cell orientation, nuclear pleomorphism

• High nuclear-to-cytoplasm (N:C) ratio - hallmark feature
• Hyperchromatic, coarsely irregular nuclei
• Scant cytoplasm; cells smaller than LSIL

Biomarkers

Natural History

Clinical Implications

• Asymptomatic - detected only by screening
• HSIL cytology → mandatory colposcopy + directed biopsy
• CIN 2/3 confirmed → LEEP (preferred); cold knife cone for CIN 3/AIS suspicion
• Ablation only if invasion excluded
• Young women with p16-negative CIN 2 → conservative surveillance acceptable
• Post-treatment: remains at risk for cervical/vulvar/vaginal HPV-related cancers; long-term follow-up required

IHC in Differentiating Primary Ovarian Carcinoma from Metastatic Carcinoma

Why IHC is Needed

Step 1 - Cytokeratin Profile (First-Line Screen)

CK7 is the single most discriminatory marker separating primary ovarian from lower GI metastases. Primary ovarian carcinomas are nearly always CK7-positive, while colorectal metastases are typically CK7-negative.

Step 2 - Site-Specific Markers (Second-Line Panel)

Markers Favoring PRIMARY Ovarian Carcinoma

Markers Favoring METASTATIC Carcinoma

Differential by Clinical Scenario

Primary Ovarian (Serous) vs. Peritoneal Metastasis / Breast

• Use: PAX8 + WT1 + ER
• HGSC: PAX8(+), WT1(+), ER(+/-), CK7(+), CK20(−)
• Breast metastasis: GCDFP-15(+), mammaglobin(+), GATA3(+), PAX8(−), WT1(−)

Primary Ovarian (Mucinous) vs. Colorectal / Appendiceal Metastasis

• Most difficult differential
• Use: CK7 + CDX2 + CK20
• Primary ovarian mucinous: CK7(+), CDX2 negative or focal, CK20 variable
• Colorectal: CK7(−), CDX2(+), CK20(+) - classic "colorectal profile"
• Appendiceal: similar to colorectal; may also express CDX2

Primary Ovarian (Clear Cell) vs. Metastatic Renal Cell Carcinoma

• Use: CK7 + CA-125 + CD10 + PAX8 + RCC marker + vimentin
• Primary ovarian clear cell: CK7(+), CA-125(+/-), CD10(−), PAX8(+), vimentin(−)
• Renal clear cell: CD10(+), RCC(+), CK7(−), vimentin(+), PAX8(+)
• Note: PAX8 is positive in both - it cannot discriminate here; use CD10 + CK7

Primary Ovarian (Endometrioid) vs. Metastatic Colorectal

• Use: CK7 + CDX2 + ER + β-catenin (nuclear)
• Ovarian endometrioid: CK7(+), ER(+), CDX2(−), nuclear β-catenin(+/−)
• Colorectal: CK7(−), CDX2(+), ER(−), nuclear β-catenin(+)

Summary Panel Algorithm

Adenocarcinoma involving ovary
         │
    CK7 / CK20
         │
  ┌──────┴──────────┐
CK7+ / CK20−     CK7− / CK20+
  │                  │
Add PAX8, WT1,     CDX2 → Colorectal/
ER, GCDFP-15,      appendiceal metastasis
GATA3, TTF-1
  │
PAX8+ / WT1+ → Primary serous
PAX8+ / WT1− → Endometrioid / clear cell / renal (use CD10)
GCDFP-15+ / GATA3+ → Breast
TTF-1+ → Lung

Key Caveats

1. No single marker is absolute - IHC is always interpreted as a panel in context of morphology, clinical history, and imaging
2. PAX8 is the best single positive marker for ovarian/Müllerian origin but is also expressed in renal and thyroid tumors
3. WT1 is highly specific for HGSC but negative in mucinous, clear cell, and most non-serous primaries
4. CDX2 is superior to CK20 for detecting colorectal metastasis to ovary, but ~40% of primary ovarian mucinous tumors are CDX2-positive - limiting specificity
5. DPC4 loss is highly useful when pancreatic/biliary origin is suspected (Fishman's Pulmonary Diseases textbook)
6. Bilateral ovarian involvement, small tumors with surface implants, and signet-ring morphology (Krukenberg tumor) strongly suggest metastatic origin even before IHC

IHC: Primary Ovarian vs. Metastatic Carcinoma

Step 1 - CK7/CK20 Profile

Step 2 - Site-Specific Markers

Primary Ovarian Markers

Metastatic Markers

Key Differentials at a Glance

Caveats

• Always use a panel, never a single marker
• PAX8 is also positive in renal and thyroid carcinomas
• ~40% of primary mucinous ovarian tumors are CDX2-positive - reduces specificity
• Bilateral small ovarian tumors with surface implants = suspect metastasis regardless of IHC

Gestational Trophoblastic Disease (GTD) - Short Notes

Definition

Classification & Pathology

1. Hydatidiform Mole (Benign)

2. Invasive Mole

• Complete mole that penetrates deep into / perforates the myometrium
• Retains hydropic villi (unlike choriocarcinoma)
• Metastasizes to lung in ~15% of cases
• Develops in ~20% of complete moles after evacuation
• Not histologically malignant but clinically aggressive; responds to chemotherapy

3. Choriocarcinoma (Malignant)

• No chorionic villi (key distinguishing feature from mole)
• Sheets of anaplastic cytotrophoblasts + syncytiotrophoblasts
• Abundant, often abnormal mitoses
• Invades myometrium and blood vessels

4. Placental Site Trophoblastic Tumor (PSTT)

• Rare (<2% of GTN); from intermediate (extravillous) trophoblasts
• Secretes hPL (human placental lactogen) >> hCG - so hCG is only mildly elevated
• Resistant to chemotherapy - treatment is surgical (hysterectomy)
• Occurs after normal pregnancy or abortion

Role of Beta-hCG

Measurement tip: Assay must detect both intact hCG and free beta-subunit for optimal sensitivity in GTD monitoring.

Summary

1. Entry point - suspected GTD with elevated hCG + ultrasound
2. Molar vs. non-molar split at first branch
3. Complete vs. Partial mole differentiation by karyotype, villi extent, and hCG level
4. Post-evacuation hCG monitoring - the pivotal decision point
5. GTN branch - separates Invasive Mole, Choriocarcinoma, and PSTT/ETT with their distinct treatments
6. FIGO scoring for risk stratification driving single-agent vs. multi-agent chemotherapy
7. Footer summarizing the role of β-hCG across all stages