How is anal intraepithelial neoplasia (AIN) graded and what is the risk of progression to squamous cell carcinoma (SCC)?
- AIN is graded as low grade (AIN I or mild dysplasia) and high grade (encompasses AIN II and AIN III or moderate and severe dysplasia or carcinoma in situ, respectively).
- The term Bowen disease is used for lesions with severe dysplasia (carcinoma in situ) seen at the anal verge or perianal skin.
- The high-grade lesions are associated with high-risk human papillomavirus 16 and 18, among others. These lesions are known to recur after local treatment. The risk of progression to SCC is low (approximately 5%).