Screening for cervical cancer precursors with p16/Ki-67 dual-stained cytology: results of the PALMS study

Abstract

Background: Pap cytology is known to be more specific but less sensitive than testing for human papillomavirus (HPV) for the detection of high-grade cervical intraepithelial neoplasia (CIN2+). We assessed whether p16/Ki-67 dual-stained cytology, a biomarker combination indicative of transforming HPV infections, can provide high sensitivity for CIN2+ in screening while maintaining high specificity. Results were compared with Pap cytology and HPV testing.

Methods: A total of 27,349 women 18 years or older attending routine cervical cancer screening were prospectively enrolled in five European countries. Pap cytology, p16/Ki-67 immunostaining, and HPV testing were performed on all women. Positive test results triggered colposcopy referral, except for women younger than 30 years with only positive HPV test results. Presence of CIN2+ on adjudicated histology was used as the reference standard. Two-sided bias-corrected McNemar P values were determined.

Results: The p16/Ki-67 dual-stained cytology positivity rates were comparable with the prevalence of abnormal Pap cytology results and less than 50% of the positivity rates observed for HPV testing. In women of all ages, dual-stained cytology was more sensitive than Pap cytology (86.7% vs 68.5%; P < .001) for detecting CIN2+, with comparable specificity (95.2% vs 95.4%; P = .15). The relative performance of the tests was similar in both groups of women: younger than age 30 and 30 years or older. HPV testing in women 30 years or older was more sensitive than dual-stained cytology (93.3% vs 84.7%; P = .03) but less specific (93.0% vs 96.2%; P < .001).

Conclusions: The p16/Ki-67 dual-stained cytology combines superior sensitivity and noninferior specificity over Pap cytology for detecting CIN2+. It suggests a potential role of dual-stained cytology in screening, especially in younger women where HPV testing has its limitations.

Figure 1.

Test results and outcomes. Positive Pap cytology results are defined as atypical squamous cells of undetermined significance (ASC-US) or worse (Pap +). A positive p16/Ki-67 dual-stained cytology (Dual Stain +) is defined as the presence of one or more double- immunoreactive cell(s). A RLU/cut-off value ratio of 1.0 or higher was considered a positive test result (HPV +) for the Digene HC2 HPV DNA Test.

Figure 2.

Diagnostic performance for detecting CIN2+ (Reference standard H&E). Receiver operating characteristic graph is shown for Pap cytology (squares), dual-stained cytology (circles), and HPV (triangle) for women 18–65 years of age (gray fill), younger than 30 years (white fill), and 30 years or older (black fill).