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10 slides generated from the cancer page, with a quiz from the open benchmark and speaker notes that cite the sources. Arrow keys move between slides; Print gives one slide per page.
Anal high-grade squamous intraepithelial lesions are the HPV-driven precancer that anal cancer grows from, found by screening people at high risk with cytology and high-resolution anoscopy. The ANCHOR trial showed that treating these lesions, mostly by ablation in the clinic, cuts the number that become anal cancer, so screening and treatment are now recommended for people living with HIV.
Anal high-grade squamous intraepithelial lesions (HSIL, formerly anal intraepithelial neoplasia grades 2 and 3) are the precursor of anal squamous cell carcinoma in the same way that cervical HSIL precedes cervical cancer, and are caused by the same persistent high-risk HPV types, above all HPV 16. They are commonest in people living with HIV, in transplant recipients and in women with a history of cervical, vaginal or vulvar HPV disease. They cause no symptoms and are found by anal cytology followed by high-resolution anoscopy with biopsy, the anal equivalent of colposcopy, and p16 immunohistochemistry helps the pathologist separate HSIL from low-grade change.
Whether treating HSIL prevents cancer was uncertain until the ANCHOR trial (New England Journal of Medicine 2022) randomised 4,459 people living with HIV to treatment or active monitoring: treatment, mostly office-based electrocautery or infrared coagulation with topical fluorouracil or imiquimod for extensive disease, reduced progression to anal cancer by 57 percent. On that evidence the 2024 International Anal Neoplasia Society guidelines recommend screening from age 35 for men who have sex with men and transgender women living with HIV and from 45 for other people with HIV, and HPV vaccination remains the primary prevention. Lesions recur often after treatment, so surveillance continues, and biomarkers such as HPV 16 typing and methylation markers are being studied to decide which lesions most need treatment.
| Setting | Approach | Guideline |
|---|---|---|
| Screening | Anal cytology or high-risk HPV testing followed by high-resolution anoscopy in people living with HIV and other high-risk groups, following the 2024 International Anal Neoplasia Society guidelines. | not mapped |
| Treatment of HSIL | Office-based ablation (electrocautery, infrared coagulation) for discrete lesions; topical fluorouracil or imiquimod for extensive or perianal disease; excision for lesions where invasion is suspected (ANCHOR). | not mapped |
| Prevention | HPV vaccination, which protects against the HPV types that cause almost all anal cancer. | not mapped |
| After treatment | Repeat high-resolution anoscopy because recurrence is common; biopsy of any lesion that changes or ulcerates. | not mapped |