New Terminology for Cervical Intraepithelial Neoplasia (CIN)
The term Cervical Intraepithelial Neoplasia (CIN) is now also referred to as Squamous Intraepithelial Lesion (SIL) in modern classification systems, with CIN terminology remaining in use for histologic diagnosis while SIL terminology is primarily used in cytologic reporting. 1
Dual Terminology Systems
The evolution of cervical precursor lesion terminology has resulted in two parallel classification systems that are both currently in use:
Histologic Classification (CIN System)
- CIN 1 corresponds to mild dysplasia and is classified as low-grade SIL 1
- CIN 2 corresponds to moderate dysplasia and is classified as high-grade SIL 1
- CIN 3 corresponds to severe dysplasia/carcinoma in situ and is classified as high-grade SIL 1
Cytologic Classification (Bethesda System - SIL)
- Low-grade Squamous Intraepithelial Lesion (LSIL) encompasses CIN 1 and lesions showing clear evidence of papillomavirus effect 1
- High-grade Squamous Intraepithelial Lesion (HSIL) encompasses CIN 2 and CIN 3 1
Important Distinctions Between Systems
It is critical to understand that cytological LSIL is not equivalent to histological CIN 1, and cytological HSIL is not equivalent to histological CIN 2/3. 2, 3 These represent different diagnostic modalities with different predictive values and should not be used interchangeably in clinical decision-making.
Two-Tiered Histologic Approach
Modern guidelines have adopted a 2-tiered histologic system that simplifies clinical management:
- CIN 1 represents low-grade lesions 2
- CIN 2,3 represents high-grade precursors, often reported together to facilitate clinical decision-making 2
This grouping reflects the biological behavior of these lesions, where CIN 2 and CIN 3 are managed similarly despite some differences in natural history 4, 3
Recent Nomenclature Refinements
The 2019 American Society for Colposcopy and Cervical Pathology (ASCCP) guidelines recommend that histological high-grade lesions be classified as CIN 2 or CIN 3 (rather than CIN 2,3 combined) to allow for the option of active surveillance of CIN 2, particularly in younger women 4
Clinical Implications
The dual terminology exists because:
- CIN terminology remains standard for histopathologic diagnosis on biopsy specimens 1, 2
- SIL terminology is used primarily in cytologic (Pap test) reporting following the Bethesda System 1
- Both systems are recognized internationally and clinicians must be fluent in translating between them 1, 5
The shift toward SIL terminology reflects improved understanding that CIN 1/LSIL represents active HPV infection rather than a true neoplastic precursor, while CIN 2,3/HSIL represents genuine precancerous lesions requiring intervention 4