| Summary: | Background: Anal HSIL ablation may reduce the incidence of invasive cancer, but few data exist on treatment efficacy in patients with delayed treatment after observation. Methods: A multisite clinical trial of HIV-positive participants (≥27 years old) with 1–3 biopsy-proven anal HSIL randomized to IRC ablation (IRC) or active monitoring (AM). After 12 months AM participants with persistent disease could be treated and followed for an additional 12 months. Initial IRC arm participants could remain on-study 12 additional months. Participants were followed every three months undergoing high-resolution anoscopy with biopsy and treatment of recurrent HSIL. Results: Of 60 participants initially randomized to AM, 35 returned for IRC at 12 m with 30 (86%) evaluable at 24 m; 25 participants (83%) achieved complete clearance (CC). Of 51 lesions treated, 41 (80%) did not recur. 80% were HSIL free (of treated/new lesions) at 24 m. The cumulative HSIL-free probability in AM participants who crossed over to treatment was 87·5+5·9% at 6 m and 63·5+9·6 at 12 m post treatment. Results did not significantly differ from the initial IRC arm. Sixteen AM participants without HSIL at 12 m continued for year 2 and 4/11 (36%) recurred by 24 m. Of 35 IRC participants who returned at 24 months, 63% maintained CC and the HSIL-free probability was 42·1+7·1% at 24 months. Conclusions: In those with limited disease, delaying ablation to allow for HSIL regression before treating remaining disease does not appear to reduce response.
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