EP644 - High Resolution Anoscopy - Establishment and Review of a Clinic-Based Practice

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Purpose/Background: The Anchor trial showed that treatment of high-grade squamous intra-epithelial lesions (HSIL) in high-risk patients prevents development of anal SCC. Consensus International Anal Neoplasia Society (IANS) 2024 guidelines recommend anal dysplasia screening and treatment in high-risk patients. Screening includes anal cytology and HPV testing; treatment is high resolution anoscopy (HRA) lesion ablation or topical treatments. High-risk conditions include HIV, history of solid organ transplant (TXP), or vulvar HSIL or SCC. Screening is recommended after age 45 for men who have sex with men (MSM) and transgender women (TGW). It can be considered in those with moderately elevated risk. Prior to starting a clinic-based program, all treatment was done in the OR. Herein we review our 1-year experience starting a clinic-based HRA program.

Methods/Interventions: A prospectively maintained, IRB approved registry was retrospectively reviewed of HRA done at our institution between September 2023 – Sept 2024. All patients are over the age of 18. Variables evaluated included demographics, dysplasia risk factors, adherence to 2016 IANS guidelines, and concordance of cytology and histology.

Results/Outcomes: 118 patients underwent 147 HRAs, 102 (69.4%) done in clinic. HRA was done in the OR based on patient preference, anticipated clinic intolerance, burden of disease, or combined procedure. The average age was 52.9 years (range 25.5-84.0). 58 (49.2%) patients were assigned female sex at birth, 60 (50.8%) male sex at birth, 4 (3.4%) were TGW; no patients identified as non-binary. 109 (92.4%) patients had at least one high risk factor, 9 (7.6%) had only moderate risk factors. There were 46 (39.0%) MSM. There were 29 (24.6%) patients with HIV, 80 (67.8%) had a history of high-risk anal HPV, 48 (40.7%) with history of anal HSIL or SCC, 14 (11.9%) with TXP.
Comparison with IANS guidelines is found in Table 1. There were 69 histologic diagnoses of HSIL (hHSIL) in 53 patients. A total of 17 anal pap exams showed cytologic HSIL (cHSIL) (13 unique patients), with hHSIL in 16 cases. The remaining one had histologic low-grade squamous intra-epithelial lesion (LSIL). hHSIL was preceded by cHSIL in 16 (23.2%) cases, atypical cells with high-risk features (ASCH) in 13 (18.8%); 21 (30.4%) had cells of uncertain significance (ASCUS), 8 (11.6%) cLSIL, 3 (4.3%) negative for pathology (cNILM), and 2 (2.9%) had unsatisfactory samples.
There were 8 cases of cLSIL with HRA finding hHSIL. ASCH was found on 22 anal pap exams, with hHSIL subsequently identified in 13 cases. Of 67 total hHSIL cases, 45 (67.2%) were identified on HRA in clinic, 22 (32.8%) in the OR.

Conclusion/Discussion: We started a clinic-based HRA practice to increase the patient volume we can treat in a lower resource setting. We found that clinic-based HRA was well tolerated, and our practice is generally concordant with IANS guidelines. One patient with cHSIL on anal pap had hLSIL on subsequent HRA; they were reevaluated at 8 months, beyond the recommended 6 month. Another area for improvement is recall of patients with cHSIL for HRA within 3 months. A variety of providers perform cytologic screening at our institution, and we are working in a multidisciplinary team to improve this metric. Regarding concordance of cytology and histology, most cases of cHSIL or ASC-H had hHSIL. However, 58.0% of patients with lesser cytology had hHSIL, reinforcing the known issue of anal cytology failing to detect HSIL when present. We safely implemented a HRA clinic, allowing us to treat more patients with anal dysplasia while also liberating OR time.