Degenerated keratinized tumor cells in oropharyngeal human papilloma virus-associated squamous cell carcinoma: A pitfall in p16 immunostaining of fine-needle aspiration specimens

Objective: High-risk human papilloma virus (HPV) testing should be performed on all patients with newly diagnosed oropharyngeal HPV-associated squamous cell carcinoma (OPHPVSCC), and p16 immunostaining can be used as a surrogate marker. Although in surgical pathology specimens p16 staining in > 70% of the tumor cells is considered a positive result, the interpretation in fine-needle aspiration (FNA) specimens has remained controversial. Study Design: FNA of neck lymph nodes and corresponding surgical specimens from 42 patients with OPHPVSCC were reviewed. Results: In FNA specimens, 38 cases (90.5%) had viable tumor cells, 32 (76.2%) had keratin debris, and 36 (85.7%) had degenerated keratinized tumor cells. Twenty-seven of 27 (100%) had positive p16 staining in > 70% of viable tumor cells, while the degenerated tumor cells were negative. Twenty of 24 (83.3%) primary OPHPVSCC exhibited focal degenerated keratinized tumor cells and/or keratin debris. Conclusions: This study showed that the majority of the OPHPVSCC metastases in lymph nodes had degenerated keratinized tumor cells and keratin debris. Many primary OPHPVSCC also demonstrated focal keratinization and/or degeneration. The degenerated tumor cells showed no immunoreactivity to p16. The same 70% cutoff used in histologic specimens should be applied in cytologic specimens, but only the viable tumor cells should be counted.