90 p16 IHC Validation on Cytology Cell Blocks. (11th January 2018)

• Record Type: Journal Article
• Authors: Shirsat, Hemlata; Bullock, Martin; Hache, Kelly Dakin; Hart, Robert; Rigby, Matthew
• Is Part Of: American journal of clinical pathology. Volume 149(2018)Supplement 1
• Page Start: S38
• Page End: S39
• Publication Date: 2018-01-11
• Subjects: Diagnosis, Laboratory -- Periodicals; Pathology -- Periodicals; 616.07
• DOI: 10.1093/ajcp/aqx117.089
• Languages: English
• ISSNs: 0002-9173

Abstract

Abstract: Background: P16 immunohistochemistry (IHC) is a reliable surrogate marker for human papillomavirus (HPV) causation in oropharyngeal squamous cell carcinoma (OPSCC) and is requested on neck FNA. However, p16 IHC is not validated on cytology cell blocks with no established interpretation guidelines. Objective: The current study compared p16 IHC in cytology and surgical specimens, to devise criteria for accurate p16 evaluation in cytology cell blocks to ensure close to 100% specificity of a positive result. Method: p16 IHC was examined in 27 matched FNA and surgical cases of OPSCC over a two-year period. Fifty viable basaloid tumor cells in clusters were considered adequate. Both cytoplasmic and nuclear staining was evaluated. Extent of nuclear p16 staining was scored as <25%, 25%-50%, 50%-75% or >75%; intensity was scored as mild, moderate, or intense. Results: Three of 27 were p16 negative on both the cytology and surgical specimens, and served as negative controls. The remaining 24 cases were p16 positive on the surgical specimens. Eight were excluded due to low cellularity or presence of only desquamated individual keratinized tumor cells. Six of 27 showed >75% cells with weak-intense nuclear staining. Three of 27 showed 50%-75% cells with weak-intense nuclear staining. One of 27 had weak nuclear staining in <25% cells. Three of 27 showed only weak cytoplasmic staining. Three of 27 had no nuclear or cytoplasmic staining. Conclusion: At least 50 viable basaloid cells in small groups should be assessed. Cells with any cytoplasmic staining should be evaluated for nuclear staining. A threshold of 25% nuclear staining results in a specificity of 100%.