Cervical intraepithelial neoplasia (CIN) progresses through grades 1-3 based on the extent of dysplastic cells occupying the epithelial thickness. CIN 3 (severe dysplasia/carcinoma in situ) is defined by dysplastic cells involving:
- A Full thickness of the epithelium without invasion through the basement membrane ✓
- B Lower third of the epithelium only
- C Lower and middle thirds of the epithelium
- D Invasion through the basement membrane into the stroma
Correct answer: A. Full thickness of the epithelium without invasion through the basement membrane
Explanation
CIN grading reflects progressive loss of normal maturation. CIN 1 involves the lower third; CIN 2 involves the lower two-thirds; CIN 3 (carcinoma in situ) shows full-thickness dysplasia with mitoses at all levels and no surface maturation, but the basement membrane remains intact. Invasion through the basement membrane defines microinvasive or invasive squamous cell carcinoma and is no longer CIN.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.