HPV-associated disease of the anal canal: A pathology primer

Anal cancer is a rare disease. Screening for it in high-risk populations is based on the model borrowed from cervical cancer screening with cytology and high-resolution anoscopy-guided biopsy. Squamous cell carcinoma of the anus is associated with oncogenic HPVs, particularly type 16. Squamous intraepithelial lesions (SIL) are graded on both anal cytology and histology using 2 tiers. Low-grade SIL is reflective of a productive HPV infection; high-grade SIL is the potential precancer. High-risk HPV testing may not be an efficient screening or triage tool given the high prevalence of the virus in populations targeted for anal cancer screening. However, genotyping for HPV 16 may prove useful. On biopsy, p16 immunostaining is used to adjudicate equivocal diagnoses on routine H&E tissue sections; a positive p16 immunostain supports a diagnosis of high-grade SIL.