Abstract 433: Utility of p16 immunohistochemistry in evaluating negative cervical biopsies following high-risk pap test results
Authors: Shain Alana F. , Kwok Shirley , Folkins Ann K. , Kong Christina S. 
Published: July 2016

Abstract
The Lower Anogenital Squamous Terminology (LAST) Standardization Project for HPV-associated Lesions recommends the use of p16 immunohistochemistry as an adjunct to morphologic assessment of cervical biopsies interpreted as negative from patients that are at high risk for missed high-grade disease (defined as a prior cytologic interpretation of HSIL, ASC-H, ASC-US/HPV-16+, or AGC-NOS) (Darragh et al., 2012). However, few studies have specifically evaluated the utility of performing p16 on negative cervical biopsies and endocervical curettage specimens following high-risk Pap test results.
A search of the Stanford Cytopathology database from 7/1/2002-6/30/2012 for cervical cytology cases with diagnoses of ASC-H, HSIL, AGC-NOS, and atypical endocervical cells NOS (AGC-EC) yielded 1517 cases. Of these, 703 cases had histologic follow-up. Biopsies were excluded if diagnosed as atypical, low grade squamous intraepithelial lesion (LSIL), high grade squamous intraepithelial lesion (HSIL), or insufficient, or if the time to follow up was greater than 1 year. Immunostain for p16 (CINtec) was performed on 350 cases from 339 patients (age 16-85 yrs, average 42+/-14) and scored as positive (diffuse strong), negative or equivocal. 6 cases were excluded due to insufficient tissue and 3 cases with equivocal staining were excluded from further analysis. For p16(+) and equivocal cases, HPV in situ hybridization (ISH) (Ventana HPV III Family 16 probe) was performed and the corresponding H&E section reviewed. Based on the H&E review, the diagnosis was revised. Follow-up data was also obtained.
12/341 cases (3.5%) were p16(+) corresponding to missed diagnoses of LSIL (1 cases), HSIL-CIN2 (2 cases), and SIL-indeterminate grade (6 cases). Two biopsies from one patient at different time points exhibited p16 staining of bland metaplastic cells undermining endocervical glands that morphologically did not meet criteria for SIL and were interpreted as atypical metaplasia. Follow-up biopsies showed HSIL.
p16 immunostain increases the detection rate of SIL by 3.5% in benign appearing cervical biopsies and endocervical curettages from patients with a prior high-risk Pap test result. The benefit of p16 immunostain is highest for cases with a prior Pap diagnosis of HSIL. Cytoplasmic only staining and staining of surface mucosa, endocervical glands, and tubal metaplasia may lead to over-interpretation of p16 as positive.
Reference:
Darragh, T. M. et al. The Lower Anogenital Squamous Terminology Standardization Project for HPV-Associated Lesions: background and consensus recommendations from the College of American Pathologists and the American Society for Colposcopy and Cervical Pathology. Arch. Pathol. Lab. Med. 136, 1266-1297 (2012).
Citation Format: Alana F. Shain, Shirley Kwok, Ann K. Folkins, Christina S. Kong. Utility of p16 immunohistochemistry in evaluating negative cervical biopsies following high-risk pap test results. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 433.