P16INKa Immunocytochemistry in Fine-needle Aspiration Cytology Smears of Metastatic Head and Neck Squamous Cell Carcinoma

Objectives: Patients with head and neck squamous cell carcinoma (HNSCC) may initially present with neck metastases diagnosed by fine-needle aspiration (FNA). In these patients, it is critical to locate the primary site so that targeted therapy can be administered. Nearly a quarter of HNSCC are associated with human papillomavirus (HPV) infection. The great majority of HPV-related primaries originate in the oropharynx. p16INKa (p16) functions as a surrogate marker of HPV infection. We sought to determine if expression of p16 by immunocytochemistry (ICC) in neck metastases could assist in localizing the primary site to the oropharynx.

Study Design: Diagnostic FNA cytology smears of neck metastases from 90 patients with biopsy-proven primary HNSCC were reviewed. Papanicolaou-stained slides were directly subjected to ICC, using p16 antibody.

Results: Twenty-seven (30%) tumors expressed p16 by ICC; 74% of these p16-positive tumors were metastases from oropharynx. There was a significantly higher proportion of p16 expression in patients with primary oropharyngeal carcinoma (47%) versus those whose primary tumor was non-oropharyngeal (15%; p = 0.0013).

Conclusions: p16 expression in FNA cytology smears of metastatic HNSCC is a useful indicator of oropharyngeal origin and can be used to help localize the primary site in cases where this is not clinically evident.