Anal intraepithelial neoplasia: correlation of grade with p16INK4a immunohistochemistry and HPV in situ hybridization.

Accurate diagnosis and grading of anal intraepithelial neoplasia (AIN) can be problematic, especially in separating AIN from anal transitional-zone epithelium. Immunohistochemistry (IHC) for p16 correlates with human papillomavirus (HPV) integration into the host genome, and HPV subtyping by in situ hybridization (ISH) is now readily available. To investigate if p16 would help in more accurately diagnosing and grading AIN, particularly when attempting to distinguish benign transitional-zone epithelium from high-grade AIN, we separately assessed these stains in a blinded manner on a large number of consecutive anal biopsies and anal tissues and correlated the findings with the diagnosis and grade of AIN.