p16 Immunohistochemical Expression in Squamous Metaplasia of Endocervical Polyps
V Dube, S Nofech-Mozes, N Ismiil, RS Saad, Z Ghorab, MA Khalifa. Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Canada
Background: The immunohistochemical antibody directed against p16 is regarded as a surrogate marker for high-risk HPV infection and is used to differentiate between high-grade squamous intraepithelial lesions (HSIL) and their benign mimics. Endocervical polyps often have metaplastic squamous epithelium which may show reactive changes that can mimic HSIL. The aim of this study is to characterize the p16 immunoprofile of reactive squamous metaplasia in endocervical polyps.
Design: In-house cases of endocervical polyps accessioned between September 2007 and May 2008 were retrieved from the pathology archives. All slides were reviewed and cases with squamous epithelium were classified into two categories: polyps with reactive squamous metaplasia and polyps with mature, non-dysplastic squamous epithelium. The latter group served as a negative control. Sections were stained with p16ink4a and ki-67. Staining for p16 was recorded as positive when it showed strong and diffuse nuclear staining and/or cytoplasmic staining in at least the parabasal cells. Increased proliferation revealed by ki-67 immunostaining was evaluated in p16-positive cases, to exclude HSIL.
Results: We identified 164 consecutive cases of cervical biopsies or hysterectomies with benign endocervical polyps. 44 of the 164 polyps showed squamous epithelium and were included in the study. 19/44 were categorised as polyps with reactive squamous metaplasia and 31/44 as polyps with mature squamous epithelium (6 polyps showed both reactive and mature epithelium). P16 was positive in 8/19 (42.1%) polyps with reactive squamous metaplastic epithelium and in only 4/31 (12.9%) polyps with mature squamous epithelium. This difference was statistically significant using the chi-square test (p value = 0.019) and the Fisher exact test (p value = 0.038). None of the cases positive for p16 showed increased proliferation with ki-67. Furthermore, only one patient with a polyp showing reactive squamous metaplasia had a known history of HPV infection (low grade squamous intraepithelial lesion diagnosed 7 years earlier).
Conclusions: Our immunohistochemical results reveal that reactive squamous metaplasia of endocervical polyps can be positive for p16 in a significant proportion of the cases. This information is important to bear in mind in order not to overdiagnose HSIL in these cases. In cases positive for p16, staining with ki-67 is useful to exclude squamous intraepithelial lesion.
Monday, March 9, 2009 1:00 PM
Poster Session II # 138, Monday Afternoon