[714] P16 and Ki-67 Immunostaining as Markers of Anal Intraepithelial Neoplasia and Condyloma – Correlation with Human Papillomavirus Detection by PCR

EC Pirog, KD Quint, RK Yantiss. Weill Medical College of Cornell University, New York, NY; DDL Diagnostic Laboratory, Voorburg, Netherlands

Background: The classification of anal intraepithelial neoplasia (AIN) in mucosal biopsies is subject to considerable interobserver variability. Ki-67 and p16 immunostains have been shown to aid the diagnosis of squamous neoplasia in biopsy samples from the uterine cervix. Thus, the aim of this study was to evaluate the utility of Ki-67 and p16 immunostaining as adjunct tests to increase diagnostic accuracy.
Design: 75 consecutive anal biopsies originally diagnosed as benign anal transitional zone (NEG, n=15), fibroepithelial polyp (FEP, n=10), condyloma accuminatum (CONA, n=10), low-grade AIN (AIN1, n=20), and high-grade AIN (10 cases AIN2 and 10 cases AIN3) were collected. All cases were re-reviewed to obtain a consensus diagnosis and all cases were tested for HPV DNA by SPF10 PCR and LIPA25 genotyping assay. The results of HPV testing were correlated with consensus diagnosis to reach a final classification. All cases were immunostained for Ki-67 and p16. Ki-67 positivity was defined as a cluster of at least two positive nuclei in the upper two-thirds of the epithelial thickness. A postitive result for p16 was defined as moderate to strong intensity nuclear and cytoplasmic staining.
Results: Histologic review and HPV testing led to reclassification of 16 cases, so that the final study group included 17 NEG, 14 FEP, 6 CONA, 11 AIN1, 16 AIN2, and 11 AIN3. All cases of CONA and AIN were positive for HPV, whereas all FEPs were negative for HPV by PCR. All NEG cases and FEPs were negative for both Ki-67 and p16. All CONA and AIN1 cases were positive for Ki-67, but negative for p16. All cases of either AIN2 or AIN3 were positive for Ki-67 and p16. Overall, the sensitivity and specificity of Ki-67 for detection of anal condyloma or AIN was 1.0 and 1.0, respectively. The sensitivity and specificity of p16 for detection of AIN2 or AIN3 was 1.0 and 1.0, respectively.
Conclusions: Ki-67 is a highly sensitive and specific marker for detection of HPV-related changes and neoplasia in the anal mucosa, whereas p16 staining is strongly associated with high-grade squamous neoplasia. These results indicate that a combination of these markers may aid interpretation of anal mucosal biopsy samples.
Category: Gastrointestinal

Tuesday, March 23, 2010 9:30 AM

Poster Session III # 129, Tuesday Morning

 

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