Validation of p16 immunocytochemical staining on alcohol-fixed aspirate smears: A single-institutional study with review of the literature.

BACKGROUND

Determining human papillomavirus (HPV) status in oropharyngeal squamous cell carcinoma can have a significant impact on treatment and clinical outcomes. Because fine-needle aspiration (FNA) is typically an initial diagnostic modality in a patient workup for primary or suspected metastatic disease, immunostaining for p16 on FNA material is a promising option to determine HPV tumor status, possibly avoiding biopsies or excisions. In this study, the authors investigated the possibility of using alcohol-fixed smears as a reliable alternative for reporting p16 status.

METHODS

Twenty HPV-associated tumors and 20 non-HPV-associated tumors were identified using the gold-standard histologic cutoff for positivity of ≥70% strong nuclear and cytoplasmic staining. Matched FNA specimens were identified for comparison staining, and a positive p16 result was rendered on a single aspirate smear using the same cutoff of ≥70%.

RESULTS

On alcohol-fixed cytology smears, 16 of 20 (80%) HPV-associated tumors showed positive p16 staining in ≥70% tumor cells. Four cases showed lower level (30%-60%) nuclear and cytoplasmic staining. Nineteen of 20 (95%) non-HPV-associated tumors showed no or minimal p16 staining (0%-10%), and 1 case had a p16-equivocal cytology result.

CONCLUSIONS

The authors performed immunocytochemical validation for p16 using alcohol-fixed smears and observed promising results, offering this technique as a potential alternative to formalin-fixed tissue in the appropriate clinical context. By using a positive staining cutoff of ≥70%, this technique offers 80% sensitivity and 95% specificity for detecting HPV-associated tumors. Although it was not performed in the current study, HPV-specific testing on available formalin-fixed, paraffin-embedded tissue should be considered in cases with equivocal or negative p16 staining.