[1225] p16 Expression in Squamous Cell Carcinomas from Non-Cervical Primary Sites: An Immunohistochemical Study of 100 Cases

EE Doxtader. State University of New York Upstate Medical University, Syracuse, NY

Background: p16 is a cell-cycle regulatory protein that is upregulated in cells infected with oncogenic subtypes of human papillomavirus (HPV). Recent studies have suggested a role for p16 immunohistochemistry in determining the site of origin in cases of squamous cell carcinoma (SQCCA) of unknown primary. The aim of this study is to determine the incidence of p16 expression in SQCCAs from various sites (other than cervix, where most SQCCA are known to express p16) in order to assess the utility of p16 immunohistochemistry in determining the primary site of origin of cases of metastatic SQCCA.
Design: 100 cases of SQCCAs from 5 major primary sites including 20 each from lung, esophagus, tonsil, non-tonsillar head and neck and skin were retrieved from our surgical pathology archives. The histological features were reviewed. p16 immunohistochemistry was performed on a representative block from each case. Cases were considered positive if strong nuclear and cytoplasmic staining was detected in more than 10% of cells.
Results: p16 expression was detected in 47/100 (47%) cases overall, and was found in all primary sites tested, including tonsil (15/20, 75%), skin (9/20, 45%), non-tonsillar head and neck sites (8/20, 40%), lung (8/20, 40%), and esophagus (7/20, 35%). Of the non-tonsillar head and neck sites, the highest proportion of positive cases was from the nasopharynx (4/5, 80%). Most positive cases expressed p16 in greater than 90% of cells (36/47), with fewer cases showing expression in 50-90% (6/47) or 10-50% (5/47) of cells. Proportion of cells staining did not correlate with primary site or with degree of differentiation of the tumor.
Conclusions: p16 is expressed in SQCCAs from a wider variety of primary sites than generally appreciated. In addition to tonsillar SQCCAs, a large proportion of which are known to express p16, SQCCAs of the lung, esophagus and non-tonsillar head and neck sites commonly express p16. p16 expression therefore cannot be reliably used to establish the site of origin. Our findings additionally raise the possibility of HPV infection in the pathogenesis of SQCCAs of a wide variety of sites. Further investigation is needed to determine the correlation between p16 expression and HPV infection in these sites.
Category: Head & Neck

Tuesday, March 23, 2010 1:00 PM

Poster Session IV # 155, Tuesday Afternoon

 

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