Interlaboratory concordance of p16/Ki-67 dual-staining interpretation in HPV-positive women in a screening population

Background: p16/Ki-67 dual staining is a candidate biomarker for triaging human papillomavirus (HPV)–positive women. Reproducibility is needed for adopting a test for screening. This study assessed interlaboratory reproducibility in HPV-positive women. Methods: All women positive for HPV from the Italian New Technologies for Cervical Cancer 2 study, were included in this study. ThinPrep slides were immunostained for p16/Ki-67 in 4 laboratories and were interpreted in 7 laboratories. Each slide had 3 reports from different laboratories. Slides were classified as valuable or inadequate, and valuable slides were classified as positive (at least 1 double-stained cell) or negative. Interlaboratory reproducibility was evaluated with κ values. Results: Overall, we obtained 9300 reports for 3100 cases; 905 reports (9.7%) were inadequate. The overall adequacy concordance was poor (κ = 0.224; 95% confidence interval [CI], 0.183-0.263). The overall positivity concordance was moderate (κ = 0.583; 95% CI, 0.556-0.610). Of the 176 cervical intraepithelial neoplasia 2+ (CIN-2+) lesions found in HPV DNA–positive women, 158 had a valid result: 107 were positive in all 3 reports (sensitivity for CIN-2+, 67.7%; 95% CI, 59.8%-74.9%), 23 were positive in 2 reports (sensitivity of the majority report, 82.3%; 95% CI, 75.4%-87.9%), and 15 were positive in 1 report (sensitivity of at least 1 positive result, 91.8%; 95% CI, 86.3%-95.5%). Thirteen CIN-2+ cases were negative in all 3 reports. The overall positivity concordance in CIN-2+ samples was κ = 0.487 (95% CI, 0.429-0.534), whereas in the non–CIN-2+ samples, it was κ = 0.558 (95% CI, 0.528-0.588). Conclusions: The p16/Ki-67 assay showed poor reproducibility for adequacy and good reproducibility for positivity comparable to that of cervical cytology. Nevertheless, the low reproducibility does not affect the sensitivity for CIN-2+.