Detection of anal squamous dysplasia at routine colonoscopy in 121 patients: implications for anal cancer screening

Anal squamous cell carcinoma and its precursors, squamous intraepithelial lesions, arise in the anal transitional zone and pecten-a segment traversed during every colonoscopy. Whether conscious inspection of these areas during routine colonoscopy enhances detection of anal dysplasia has not been established.

An observational analysis (2011-2025) was conducted within a single academic health system, involving adult patients undergoing screening or diagnostic colonoscopy. Squamous anal dysplastic lesions seen in the anal transitional zone and pecten were photographed and biopsied. Specimens were classified as low-grade squamous intraepithelial lesions, high-grade squamous intraepithelial lesions, or squamous cell carcinoma. Demographics, colonoscopy indications, and recognized risk factors were recorded.

Incidental anal neoplasia was identified in 121 patients (71 female, 49 male, one transgender; median age 59 years [range 39-82]). Endoscopists detected 64 low-grade squamous intraepithelial lesions, 52 high-grade squamous intraepithelial lesions, and 5 squamous cell carcinomas, representing 52.9%, 43.0%, and 4.1% of lesions, respectively. Thirty-eight endoscopists made these findings during colonoscopies performed for colorectal cancer screening, polyp surveillance, or common gastrointestinal complaints. Conventional high-risk conditions, including human immunodeficiency virus infection, anogenital intraepithelial neoplasia, or organ transplantation, were present in 41 (33.9%) patients. Representative endoscopic images of anal dysplastic lesions are included.

A brief, deliberate inspection of the anal transitional zone and pecten during colonoscopy consistently reveals anal squamous intraepithelial lesions and squamous cell carcinoma. Incorporation of this maneuver into standard colonoscopy practice could extend early detection of anal dysplasia beyond presently targeted high-risk groups and thereby reduce the overall burden of anal cancer.