Abstract
Fine-needle aspiration (FNA) of a neck mass is frequently the initial diagnostic procedure for patients with human papillomavirus-positive head and neck squamous cell carcinoma. By performing a p16 immunocytochemistry (ICC) stain on FNA material, the pathologist can help to direct the treating physician's search for the primary site and to select the proper management for the patient. There is currently no established threshold for the evaluation of p16 ICC in cytology samples. This study was aimed at establishing an optimal threshold for p16 ICC interpretation in cytology samples.
The pathology databases were searched for all neck-mass FNAs diagnosed as squamous cell carcinoma from January 2010 to March 2019. p16 ICC was performed on cytology smears, and the percentage and intensity of p16-positive cells were assessed. Receiver operating characteristic (ROC) curves were plotted to determine the best cutoff threshold for p16 positivity on cytology smears.
p16 ICC was performed on 50 cytology smears. An analysis of 8 different thresholds (combinations of the percentage and intensity of the p16 stain) using ROC curves demonstrated the best threshold to be 50% p16 staining with a sensitivity of 74% and a specificity of 100%. Applying the threshold used for surgical specimens (70%) to cytology samples resulted in a low sensitivity (45%).
p16 ICC on cytology smears shows diminished staining in comparison with surgical samples. Using 50% staining as the cutoff to consider positivity for p16 in cytology smears is proposed to decrease false-negative results while maintaining specificity.
