A 28-year-old woman presents to the gynaecology clinic with abnormal vaginal bleeding and postcoital spotting for 3 months. On speculum examination, a friable, bleeding cervical lesion is noted. Pap smear shows atypical squamous cells of undetermined significance (ASCUS). HPV testing is positive for high-risk HPV-16. Colposcopy with biopsy reveals cervical intraepithelial neoplasia grade 2 (CIN2). Which of the following best explains the mechanism by which HPV-16 leads to malignant transformation in this patient?

Explanation

## Mechanism of HPV-Mediated Malignant Transformation ### HPV Oncoproteins and Tumour Suppressors **Key Point:** High-risk HPV types (16, 18, 31, 33) encode two critical oncoproteins — E6 and E7 — that directly inactivate the two most important cellular tumour suppressors: p53 and retinoblastoma (Rb) protein. **High-Yield:** - **E6 oncoprotein** binds to and promotes proteasomal degradation of p53 (the "guardian of the genome"), preventing apoptosis and cell cycle arrest in response to DNA damage. - **E7 oncoprotein** binds to and inactivates Rb protein, disrupting the G1/S checkpoint and allowing uncontrolled cell cycle progression. ### Pathogenic Cascade 1. Persistent infection with high-risk HPV (especially types 16 and 18) 2. E6/E7 expression → p53 and Rb inactivation 3. Loss of apoptosis and cell cycle control 4. Accumulation of additional mutations 5. Progression from CIN1 → CIN2 → CIN3 → invasive carcinoma ### Clinical Correlation in This Case The patient's CIN2 lesion represents intermediate dysplasia driven by HPV-16 E6/E7 activity. Without intervention (excisional treatment), approximately 30% of CIN2 lesions progress to invasive cancer within 5 years [cite:Park 26e Ch 7]. **Clinical Pearl:** HPV-positive ASCUS with high-risk HPV type (16 or 18) carries a significantly higher risk of underlying CIN2/3 compared to HPV-negative ASCUS, justifying colposcopy referral — as demonstrated in this case. ### Comparison with Other Viral Oncogenic Mechanisms | Mechanism | HPV | HBV | EBV | HTLV-1 | |-----------|-----|-----|-----|--------| | Direct p53/Rb inactivation | Yes (E6/E7) | No | No | No | | Integration-driven instability | Rare in CIN | Common | Rare | Rare | | Reverse transcriptase | No | Yes | No | Yes | | Immune evasion primary | No | Yes | Yes | No | **Mnemonic:** **E6 and E7 are the Evil oncoproteins** — E6 eliminates p53, E7 eradicates Rb.