CIN 3 involves the full-thickness epithelium but is distinguished from microinvasive carcinoma (Stage IA1) by the absence of:

• A Koilocytic change in the surface epithelium
• B Mitotic figures in the upper two-thirds of the epithelium
• C Stromal invasion through the basement membrane ✓
• D Positive p16 immunostaining

Explanation

CIN 3 (severe dysplasia/carcinoma in situ) involves full-thickness epithelial dysplasia with preserved basement membrane — there is no invasion into underlying stroma. The defining criterion separating CIN 3 from Stage IA1 microinvasive carcinoma is breaching of the basement membrane with stromal invasion (< 3 mm depth and < 7 mm horizontal spread for IA1). Mitotic figures, p16 positivity, and koilocytes can be seen in both CIN 3 and invasive carcinoma.

Reference: Shaw's Textbook of Gynaecology, 17th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.