Comparison between p16 Immunohistochemical Staining and HPV Testing in the Evaluation of Anal-Rectal Cytology.
Andrea N Snitchler, Jan F Silverman, Katherine M Jasnosz. Allegheny General Hospital, Pittsburgh, PA
Background: p16 immunohistochemistry (IHC) can be utilized in the evaluation of cervical biopsies for high grade dysplasia. Studies have been done on cervical cytology Pap smears showing an increased specificity of p16 while maintaining a high sensitivity, compared to high risk HPV testing (Cancer Cytopathology 2010;118(3):146-156). Although there has been only 1 prior study correlating p16 with anal-rectal cytology results (Cancer Cytopathology 2006;108(1):12-21), we believe that this is the first study evaluating p16 IHC on liquid based, anal-rectal cytology and comparing the results with high risk HPV and biopsy results.
Design: Anal-rectal cytology specimens were retrospectively collected from 2005-2010. 178 ThinPrep (Hologic, Marlborough MA) specimens were diagnosed as satisfactory for evaluation from 138 patients and 139 (78%) had concomitant HR-HPV (Digene, Germantown MD) testing. Of the 178 specimens, 59 (33%) were NILM, 69 (38%) ASCUS, 3 (1%) ASC-H, 42 (24%) LGSIL and 7 (4%) HGSIL. Biopsy results were available for 25 patients (14%). The ThinPrep slides were decolorized and the p16 IHC (CINtec, Westborough MA) was performed and evaluated blindly without knowledge of the cytology, biopsy, and HPV results.
Results: Of the anal-rectal cytology samples with known HR-HPV results, 59% of the p16 results correlated with the HR-HPV findings, while 41% of the results were discordant (p16 or HR-HPV positive with the other one negative). 71% (5/7) biopsies diagnosed as AIN2 or 3 showed p16 positivity on cytology. Positive p16 staining was present in 86% of HGSIL, 55% of LGSIL, 23% of ASCUS and 5% of NILM. The 3 ASC-H specimens were all p16 negative. The main limitations of the p16 IHC were significant background debris staining, and positive staining of basal cells causing difficulty in differentiating from p16 positive high grade dysplasia due to dark staining and obscuring nuclear morphology.
Conclusions: p16 staining of anal-rectal cytology specimens correlated with the cytology results and HR-HPV findings. However, based on our experience we believe that the value of p16 IHC may not be as useful in the evaluation of anal-rectal cytology compared to results reported for cervical Pap smears. From this study, it appears that p16 IHC staining of monolayer smears do not show any advantage over concomitant HR-HPV testing.
Tuesday, March 1, 2011 1:15 PM
Platform Session: Section D, Tuesday Afternoon