Evaluation of dual p16/Ki-67 immunostaining on anal cytology specimens

Dual immunostaining for p16/Ki67 is FDA-approved for use on liquid-based cervical cytology specimens; however, the utility of dual staining in anal cytology especially for ASCUS risk stratification is not well established.

We investigated dual staining performance on anal cytology specimens and correlated with subsequent cytologic interpretation, high-risk HPV status, and anal biopsy results. Dual staining for p16/Ki-67 was performed on all liquid-based anal cytology specimens from December 2021 to June 2022 (n = 43).

Three patients had high grade squamous intraepithelial lesion (HSIL/AIN2-3) on biopsy; dual staining was positive in all three cases. All HR-HPV negative cases were negative for dual staining. Among the 12 ASCUS samples with subsequent anal biopsy results all also had HR-HPV testing. Due to small sample size of cases with squamous intraepithelial lesion (SIL) diagnosed on biopsy, the sensitivity and positive predictive value was not calculated. However, the specificity and negative predictive value of p16/Ki-67 dual staining for SIL of any grade on biopsy were 1 (95% CI: 0.66-1) and 0.9 (95% CI: 0.65-0.97) respectively, whereas the specificity and negative predictive value of HR-HPV testing for SIL of any grade on biopsy were 0.44 (95% CI: 0.14-0.79) and 0.8 (95% CI: 0.41-0.96) respectively.

Dual p16/Ki-67 staining indicates transforming HPV infection and could help serve as an ancillary test for risk stratification for atypical anal cytology specimens. Among ASCUS samples, dual staining was specific for SIL of any grade with a high negative predictive value and therefore could be useful in clinical practices with limited availability for follow-up care.