A 28-year-old woman from Delhi presents with 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 by PCR is positive for HPV-16. Colposcopy-directed cervical biopsy reveals cervical intraepithelial neoplasia grade 2 (CIN 2). Which HPV type is most likely responsible for her cervical pathology, and what is the oncogenic mechanism?

Explanation

## HPV-16 and Cervical Oncogenesis **Key Point:** HPV-16 is a high-risk (HR) HPV type responsible for approximately 50–60% of cervical cancers and is strongly associated with CIN 2/3 and invasive cervical cancer. ### Oncogenic Mechanism **High-Yield:** The E6 and E7 oncoproteins are the critical transforming proteins in high-risk HPV: | Oncoprotein | Target | Mechanism | Consequence | | --- | --- | --- | --- | | E6 | p53 (tumor suppressor) | Binds and promotes ubiquitin-mediated degradation | Loss of apoptosis, cell cycle arrest, DNA repair | | E7 | Rb (retinoblastoma protein) | Binds and inactivates Rb | Uncontrolled G1/S transition, loss of cell cycle control | **Clinical Pearl:** HPV-16 and HPV-18 together account for ~70% of cervical cancers. HPV-16 is associated with squamous cell carcinoma, while HPV-18 is linked to adenocarcinoma. ### High-Risk vs. Low-Risk HPV Types | Feature | High-Risk (HPV-16, -18, -31, -33, -45) | Low-Risk (HPV-6, -11) | | --- | --- | --- | | E6/E7 function | Strong p53 and Rb inactivation | Weak or absent tumor suppressor interaction | | Malignant potential | High (cervical, anal, oropharyngeal cancers) | Low (benign warts, RRP) | | Integration | Frequent into host genome | Rare; usually episomal | | Clinical outcome | CIN 2/3, invasive cancer | Condyloma acuminata, benign lesions | **Mnemonic:** **HRHPV** = **H**igh **R**isk **HPV** types 16, 18, 31, 33, 45 → **H**igh potential for **C**ancer. ### Why CIN 2 Develops 1. HPV-16 infects basal epithelial cells of the cervix 2. Viral E6/E7 proteins are expressed 3. p53 and Rb are inactivated → loss of growth control 4. Accumulation of additional mutations 5. Progression from CIN 1 → CIN 2 → CIN 3 → invasive cancer (over 10–15 years if untreated) **Warning:** Low-risk HPV types (6, 11) cause benign condyloma acuminata and recurrent respiratory papillomatosis (RRP) but do NOT progress to malignancy.