Clinical overview
Cervical intraepithelial neoplasia (CIN) is the pre-invasive squamous lesion of the cervix — the window in which cervical cancer is preventable rather than merely treatable. The disease you manage at this stage is the consequence of persistent high-risk human papillomavirus (hrHPV) infection driving dysplasia of the squamous epithelium, almost always at the transformation zone. In South Africa this is not a niche problem: cervical cancer is the leading cause of cancer death in women, the incidence is among the highest in the world, and the engine behind it is a generalised HIV epidemic that accelerates HPV persistence and progression. Getting CIN management right — detecting it, grading it accurately, treating the right lesions, and not over-treating the rest — prevents more cancer deaths than almost anything else a gynaecologist does in this country.
Managing the woman who "presents with CIN" is rarely a single decision. You integrate how she was detected (screen-detected hrHPV/cytology versus colposcopic biopsy), the histological grade in WHO-2020 terms (low-grade squamous intraepithelial lesion, LSIL ≈ CIN1; high-grade squamous intraepithelial lesion, HSIL ≈ CIN2–3), her HIV status and CD4, her age and fertility intentions, her access to follow-up, and whether the colposcopy was adequate and concordant. A coherent plan answers: does this lesion need treatment now, surveillance, or excision for diagnosis — and what is the follow-up that closes the loop so a missed cancer never walks out the door. The upstream biology is covered in HPV pathology, CIN pathophysiology and Cervical carcinogenesis, and the population screening machinery in Cervical screening SA.
Core knowledge
Terminology: the two-tier WHO-2020 system and CIN equivalence
The WHO Classification of Tumours of the Female Genital Tract, 5th edition (2020), adopts the LAST/2014 two-tier nomenclature for HPV-associated squamous lesions, replacing the old three-tier CIN system. You must be fluent in both because South African laboratories and clinicians still speak in CIN:
| WHO-2020 / LAST | CIN equivalent | Biology |
|---|---|---|
| LSIL | CIN1 | Productive HPV infection; mostly transient |
| HSIL | CIN2 and CIN3 | Transforming infection; true precursor |
CIN2 is the deliberately ambiguous middle ground. Biologically it is a mix of regressing LSIL-like lesions and genuine HSIL, and reproducibility between pathologists is poor. p16 immunohistochemistry is the tiebreaker: a block-positive (diffuse, strong) p16 stain reclassifies an equivocal CIN2 as HSIL, while a negative/patchy stain supports LSIL and conservative management. This matters because over-calling CIN2 leads to over-treatment of young women whose lesions would have regressed.
Natural history and the numbers that drive decisions
LSIL/CIN1 is the cytological and histological footprint of a productive HPV infection. The majority regress — roughly 60% clear and only around 1% progress to invasion over years — which is why CIN1 is generally observed, not excised. HSIL/CIN2–3 is the transforming lesion: a meaningful proportion of untreated CIN3 (classically cited around a third or more over decades) progresses to invasive cancer, which is why HSIL is treated. The lag from persistent infection to invasion is typically a decade or more in an immunocompetent woman — the biological basis for unhurried screening intervals — but this assumption collapses in immunosuppression.
HIV: why South African CIN is different
HIV is the single most important contextual factor in South African CIN. In women living with HIV, HPV is acquired more readily, cleared less often, and progresses faster; multiple high-risk genotypes coexist; CIN is more prevalent, higher-grade, more often multifocal (involving vagina and vulva), and recurs more frequently after treatment. Recurrence/residual disease rates after excision are substantially higher than in HIV-negative women, and lower CD4 counts worsen this further. The practical consequences run through every management decision: a lower threshold to treat, awareness that ablation may be less reliable, mandatory antiretroviral optimisation (TLD — tenofovir/lamivudine/dolutegravir — per the SA HIV Clinicians Society 2023 and SA National HIV/ART Consolidated Guidelines 2023), and tighter, lifelong follow-up. Effective ART reduces but does not abolish the excess risk.