p16/Ki-67 Dual-Stain Cytology in the Triage of ASCUS and LSIL Papanicolaou Cytology Results From the European Equivocal or Mildly Abnormal Papanicolaou Cytology Study

BACKGROUND: The objective of this study was to analyze the diagnostic performance of a newly established immunocytochemical dual-stain protocol, which simultaneously detects p16(INK4a) and Ki-67 expression in cervical cytology samples, for identifying high-grade cervical intraepithelial neoplasia (CIN2+) in women with Papanicolaou (Pap) cytology results categorized as atypical squamous cells of undetermined significance (ASCUS) or low-grade squamous intraepithelial lesions (LSIL). METHODS: Residual liquid-based cytology material from 776 retrospectively collected ASCUS/LSIL cases that were available from a recent study evaluating p16 cytology and HPV testing were subjected to p16/Ki-67 dual staining. The presence of 1 or more double-immunoreactive cell(s) was regarded as a positive test outcome, irrespective of morphology. Test results were correlated to histology follow-up. RESULTS: Sensitivity of p16/Ki-67 dual-stain cytology for biopsy-confirmed CIN2+ was 92.2% (ASCUS) and 94.2% (LSIL), while specificity rates were 80.6% (ASCUS) and 68.0% (LSIL), respectively. Similar sensitivity/specificity profiles were found for both age groups of women aged < 30 years versus women aged >= 30 years. Dual-stain cytology showed comparable sensitivity, but significantly higher specificity, when compared with human papillomavirus (HPV) testing. CONCLUSIONS: The results of this study show that p16/Ki-67 dual-stain cytology provided a high sensitivity for the detection of underlying CIN2+ in women with ASCUS or LSIL Pap cytology results, comparable to the rates previously reported for HPV testing and p16 single-stain cytology. However, the specificity of this morphology-independent interpretation of p16/Ki-67 dual-stain cytology testing was further improved compared with the earlier p16 single-stain cytology approach, which required morphology interpretation, and it is significantly higher when compared with HPV testing. Cancer (Cancer Cytopathol) 2011;119158-66. (C) 2011 American Cancer Society.