HPV-associated cancers

HPV Overview - The Viral Culprit

• Structure: Non-enveloped, circular dsDNA virus with an icosahedral capsid. Highly epitheliotropic, infecting basal keratinocytes.
• Transmission: Primarily via direct contact (sexual, skin-to-skin).
• Subtypes & Risk:
  • High-Risk (Oncogenic): 16, 18, 31, 33. Associated with cervical, anogenital, and oropharyngeal squamous cell carcinoma.
  • Low-Risk (Benign): 6, 11. Cause condylomata acuminata (anogenital warts).
• Key Oncoproteins:
  • E6 → Degrades p53 (prevents apoptosis).
  • E7 → Inhibits pRb (promotes cell cycle progression).

⭐ Integration of high-risk HPV DNA into the host genome is a key event in malignant transformation. This disrupts the viral E2 gene, which normally represses the E6/E7 oncogenes.

Oncogenesis - Hijacking the Cell

• Viral Proteins Drive Malignancy: High-risk HPV (hrHPV) integrates its DNA into the host genome, leading to persistent expression of oncoproteins E6 and E7.
• E6 Protein Action:
  • Binds to and promotes the degradation of the p53 tumor suppressor protein via the ubiquitin-proteasome pathway.
  • This blocks apoptosis and cell cycle arrest, allowing damaged cells to proliferate.
• E7 Protein Action:
  • Binds to and inactivates the retinoblastoma (Rb) tumor suppressor protein.
  • This releases the E2F transcription factor, pushing the cell from G1 to S phase.

⭐ HPV types 16 and 18 are responsible for ~70% of all cervical cancers and a significant portion of other HPV-associated cancers.

Clinical Disease - Cancers & Warts

• Malignancies (High-Risk Serotypes): Associated with HPV types 16, 18, 31, 33.

  • Driven by oncoproteins: E6 (degrades tumor suppressor p53) and E7 (inhibits tumor suppressor Rb).
  • Cervical Carcinoma: Most common HPV-associated cancer.
  • Also causes squamous cell carcinoma of the anus, vagina, vulva, penis, and oropharynx.

• Benign Lesions (Low-Risk Serotypes): Caused by HPV types 6 and 11.

  • Condylomata acuminata: Anogenital warts with a cauliflower-like appearance.
  • Laryngeal Papillomatosis: Benign tumors in the larynx, can cause airway obstruction.

⭐ The E6 protein from high-risk HPV promotes the degradation of p53, while the E7 protein inactivates the retinoblastoma (Rb) protein, leading to uncontrolled cell cycle progression.

Prevention & Screening - Guarding the Gates

• Primary Prevention: Vaccination

  • Gardasil 9 (9-valent HPV vaccine) is key.
  • Routinely recommended at age 11-12; can be given from age 9 up to 45.
  • Covers HPV types 6, 11 (genital warts) and high-risk types 16, 18, 31, 33, 45, 52, 58.

• Secondary Prevention: Screening

  • Detects precancerous lesions before they become invasive cancer.
  • Methods: Pap test (cytology) & HPV DNA testing.

⭐ Pap smears begin at age 21, regardless of sexual activity onset. Co-testing (Pap + HPV DNA) is the preferred screening method for women aged 30-65.

High‑Yield Points - ⚡ Biggest Takeaways

• High-risk HPV types (16, 18) are the main cause of cervical, anogenital, and oropharyngeal cancers.
• The viral oncoprotein E6 degrades the p53 tumor suppressor, while E7 inactivates the retinoblastoma (Rb) protein.
• This disruption of key tumor suppressors bypasses cell cycle checkpoints, leading to malignant growth.
• Koilocytes-squamous epithelial cells with a wrinkled nucleus and a perinuclear halo-are pathognomonic on Pap smears.
• Primary prevention via the HPV vaccine is highly effective.