Correlation of p16 immunostaining in cell-blocks with corresponding tissue specimens for squamous cell carcinomas of the oropharynx.

OBJECTIVE: The goal of this study was to evaluate the performance of p16 staining in cell-blocks vs tissue specimens as a surrogate marker for human papillomavirus (HPV) status in oropharyngeal squamous cell carcinomas. METHODS: Head and neck squamous cell carcinoma cases presenting as a neck mass with a p16 result on cytology and corresponding tissue specimens (1 January 2014 to 30 June 1920) were included in the study. The following were assessed from cell-block material: number of tumour clusters, percentage of tumour cells with p16 staining, and presence of staining in clusters vs single cells. Results were compared to tissue p16 status. Results of any other ancillary HPV testing were also noted. RESULTS: Forty-two head and neck squamous cell carcinoma neck metastases (35 oropharyngeal, five non-oropharyngeal, and 2 unknown primaries) were identified. The p16 staining pattern in cell-blocks was seen in single cells (27.6%), clusters (44.8%), or both (27.6%). The percentage of tumour cells staining for p16 in cell-blocks was much lower than in corresponding tissue specimens. There were four false negatives and one false positive (concurrent HPV DNA polymerase chain reaction testing was positive in cytology and surgical material). CONCLUSIONS: Compared to tissue, the cut-off for p16 interpretation in cell-blocks is substantially lower and staining may be present in single cells or clusters. In 96.9% of cases, any p16 staining in cell-blocks correlated with positive p16 staining in surgical specimens. However, a negative or discrepant p16 result on cell-block should prompt confirmatory HPV studies, as false negative p16 staining in cell-blocks is high.