Staging for Cervical Intraepithelial Neoplasia (CIN)
CIN is not staged—it is graded histologically as CIN 1, CIN 2, or CIN 3 based on the extent of epithelial involvement by dysplastic cells, and this grading system is distinct from cancer staging. 1
CIN Grading System
CIN uses a three-tier histologic grading system, not a staging system like invasive cancer:
- CIN 1 (mild dysplasia): Dysplastic cells occupy the lower third of the epithelium 1, 2
- CIN 2 (moderate dysplasia): Dysplastic cells occupy the lower two-thirds of the epithelium 1, 2
- CIN 3 (severe dysplasia/carcinoma in situ): Dysplastic cells occupy more than two-thirds or full thickness of the epithelium 1, 2
The term CIN 2,3 is often used collectively because histologic distinction between moderate dysplasia and severe dysplasia/carcinoma in situ is poorly reproducible among pathologists, yet both require similar management approaches. 1
Why CIN is Graded, Not Staged
The grading system reflects the degree of epithelial maturation disruption and nuclear atypia, which correlates with cancer risk:
- CIN 1 behaves more like a productive HPV infection (often regresses spontaneously) and is now considered low-grade disease, closely resembling or identical to condyloma 2
- CIN 2,3 represents true precancerous lesions with higher progression risk: untreated CIN 3 has a 31.3% cumulative incidence of invasive cancer at 30 years, and 50.3% in those with persistent disease 3
Clinical Assessment Beyond Grading
While CIN itself is not staged, clinical assessment determines management:
- Colposcopic adequacy: Whether the entire transformation zone and lesion margins are visualized 1, 4
- Endocervical involvement: Whether disease extends into the endocervical canal (requires excisional rather than ablative treatment) 4
- Margin status: Whether CIN is present at excision margins after treatment 1, 4
- Exclusion of invasion: Excisional procedures are preferred for CIN 2,3 because occult invasive cancer occurs in 4-16% of high-grade lesions 5, 3
Common Pitfall to Avoid
Do not confuse CIN grading with FIGO staging for invasive cervical cancer. CIN represents pre-invasive disease confined to the epithelium without breaching the basement membrane. Once invasion occurs, the lesion is no longer CIN but invasive cervical cancer, which is then staged using the FIGO system (stages IA through IVB). 1, 3