Endoscopic characteristics and clinical outcomes of squamous intraepithelial lesions and squamous cell carcinoma in the anal canal.

Background and study aims: Squamous epithelial lesions, including low- and high-grade squamous intraepithelial lesions (LSILs and HSILs) and anal squamous cell carcinoma (ASCC), are rare diseases. Consequently, few reports have precisely characterized their endoscopic features or reported clinical outcomes following endoscopic submucosal dissection (ESD). In this case series, we describe detailed endoscopic characteristics and clinical outcomes of squamous epithelial lesions. Patients and methods: This was a single-center retrospective case series. Data from a consecutive series of patients who underwent ESD for squamous epithelial lesions between 2014 and 2024 were retrieved from the integrated database. Two expert endoscopists reviewed endoscopy images. Diagnostic performance of the Japan Esophageal Society (JES) classification was also investigated. Results: A total of 18 lesions from 11 patients were identified. Diagnoses after ESD were as follows: LSIL in three lesions, HSIL in 12 lesions, and ASCC in three lesions. LSILs appeared as slightly elevated lesions with whitish, papillomatous surfaces and exhibited Type A vessels. HSILs were flat or slightly elevated and showed Type B1 vessels. ASCCs presented with reddish or protruding components and exhibited Type B2 or B3 vessels at the regions. Diagnostic accuracy of JES classification was 92% (11/12; 95% confidence interval 65-99). En bloc and complete resection rates were 100% and 56%, respectively. There was no local recurrence or distant metastasis with median follow-up 12 months. Conclusions: Anal squamous epithelial lesions demonstrated characteristic findings. JES classification using magnifying narrow-band imaging might be useful, although limitations remain in detecting flat HSILs in the anal transitional zone.