Determinants of p16/Ki-67 adequacy and positivity in HPV-positive women from a screening population

Background: The objective of this study was to describe the determinants of adequacy and positivity of the p16/Ki-67 assay in a human papillomavirus (HPV)-positive screening population enrolled within the New Technologies for Cervical Cancer 2 (NTCC2) study. Methods: ThinPrep slides were immunostained for p16/Ki-67; each slide had 3 reports from different laboratories. The authors included population-related, sampling-related/staining-related, and interpretation-related variables in the analyses. Adequacy and positivity proportions were stratified by variables of interest. Univariate and multivariate logistic models were used to identify determinants of adequacy and positivity. Results: In total, 3100 consecutive HPV-positive cases were analyzed. Because every slide was interpreted by 3 centers, 9300 reports were obtained, including 905 (9.7%) that were inadequate and 2632 (28.3%) that were positive. The percentage of cases in which all 3 reports were inadequate increased with increasing age of the women and with inadequate cytology. The highest percentage of adequacy in all 3 reports and of cases with all 3 reports positive was observed in specimens from women who had grade ≥2 cervical intraepithelial neoplasia (CIN2+), atypical squamous cells of undetermined significance or more severe (ASC-US+) cytology, or mRNA positivity. The number of inadequate reports was significantly associated with increasing age, inadequate cytology, mRNA negativity, and scant cellularity. A positive p16/Ki-67 report was associated with an ASC-US+ result and with a positive mRNA result in cases both with and without CIN2+ but was associated with an HPV type 16 and/or 18 infection only in CIN2+ cases. The presence of CIN2+ was strongly associated with dual staining positivity. Conclusions: The interpretation of p16/Ki-67 results may be influenced by several different variables, all of which are part of the steps in the procedure, and by the characteristics of the screened population.