[1191] Small Biopsy Specimens Reliably Indicate p16 Expression Status of Oropharyngeal Squamous Cell Carcinoma – A Biopsy and Resection Specimen Correlation Study.

Chingqing Ma, James S Lewis. Washington University in St. Louis, MO

Background: Human papillomavirus (HPV)-related squamous cell carcinoma (SCC) is a morphologically and clinically distinct type of oropharyngeal SCC. Tumor HPV status on initial diagnostic biopsy is critical for proper management, and p16 immunohistochemistry has emerged as a reliable surrogate marker for HPV status. We sought to study if p16 staining of small diagnostic biopsies reliably predicts that of whole tumor resection specimens.
Design: From a database of oropharyngeal SCC for which p16 immunohistochemistry and histologic typing was already performed, all cases which underwent surgical resection and for which an in house primary tumor biopsy specimen was available were selected. Histologic typing was as follows: Type 1, keratinizing SCC, Type 2, hybrid SCC, and Type 3, nonkeratinizing SCC. p16 immunohistochemistry was then also performed on the diagnostic biopsy specimens. Staining was graded in the same manner on both biopsies and resections. In particular, staining was nuclear and cytoplasmic and was graded as follows: 0 = negative; 1+ = 1 to 25% of cells positive; 2+ = 26 to 50%; 3+ = 51 to 75%; 4+ = 76 to 100%.
Results: Biopsy staining results were as follows:

p16 Staining Results by Histologic Type

p16 IHC	0 (%)	1+ (%)	2+ (%)	3+ (%)	4+ (%)
All biopsies (32)	8 (25.0%)	1 (3.1%)	1 (3.1%)	1 (3.1%)	21 (65.6%)
Type 1 (9)	7 (77.8%)	1 (11.1%)	1 (11.1%)	0 (0%)	0 (0%)
Type 2 (7)	1 (14.3%)	0 (0%)	0 (0%)	1 (14.3%)	5 (71.4%)
Type 3 (16)	0 (0%)	0 (0%)	0 (0%)	0 (0%)	16 (100%)

Strictly considering the p16 score, biopsy-resection correlation was present in 28 (85.0%) of all cases including 6 (66.6%) of Type 1, 6 (85.7%) of Type 2, and 16 (100%) of Type 3 cases. Among Type 1, there were two cases that differed as p16 0 versus 1+ and one case that differed as p16 1+ versus 2+. For Type 2, the one discrepant case differed as p16 3+ versus 4+. Considering p16 expression binarily as 50% or more (3+ or 4+) being positive and lesser amounts (0, 1+, or 2+) being negative, there was perfect biopsy-resection correlation for all 32 cases. With p16 expression in resection specimens considered the gold standard, positive p16 staining in biopsies was both 100% sensitive and specific.
Conclusions: Our results demonstrate that p16 staining in diagnostic biopsies reliably reflects whole tumor staining results. p16 immunohistochemistry can be used on small diagnostic biopsies to assess for tumor HPV status.
Category: Head & Neck

Monday, February 28, 2011 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 148, Monday Morning