Background: Human-papillomavirus (HPV) testing is more sensitive, but less specific, than conventional cytology for detecting high-grade cervical intraepithelial neoplasia (CIN). We assessed whether HPV testing with triage by p16-INK4A overexpression can increase specificity while maintaining sensitivity. Methods: HPV-positive women were enrolled between June 10, 2003, and Dec 31, 2004 in a multicentre randomised controlled trial, which compared stand-alone HPV testing by Hybrid Capture 2 (experimental group) with conventional cytology, were referred for colposcopy. In seven of nine centres, cytospin preparations from these women were tested for p16-INK4A overexpression by immunostaining. The sensitivity and specificity for CIN grade 2 or more, determined at blind review of histology, were calculated for these women. We also estimated the relative sensitivity and relative referral to colposcopy that would have been obtained by HPV testing with p16-INK4A triage compared with conventional cytology. This trial is registered as a Standard Randomised Controlled Trial, number ISRCTN81678807. Findings: 24 661 women were randomly assigned to the experimental group. 1137 women (74% of those undergoing colposcopy in relevant centres), including 50 with CIN2 and 42 with CIN3 or cancer, had valid p16-INK4A immunostaining. For the endpoint of CIN2+, sensitivity and specificity of p16-INK4A (deemed positive with any number of stained cells-except endocervical, metaplastic, and atrophic cells if morphologically normal) in HPV-positive women of any age were 88% (81 of 92; 95% CI 80-94) and 61% (633 of 1045; 57-64), respectively. In the 35-60-year age group, the relative sensitivity of HPV testing and p16-INK4A triage versus conventional cytology for CIN2+ was 1·53 (95% CI 1·15-2·02) and relative referral was 1·08 (0·96-1·21). In the 25-34-year age group, relative sensitivity was 3·01 (1·82-5·17) and relative referral was 1·15 (0·96-1·37). In the latter age group, when 5% or more stained cells were deemed positive, the corresponding values were 2·06 (1·20-3·68) and 0·58 (0·46-0·73), respectively. Interpretation: HPV testing with p16-INK4A triage produces a significant increase in sensitivity compared with conventional cytology, with no substantial increase in referral to colposcopy. Funding: European Union, Italian Ministry of Health, Regional Health Administrations of Piemonte, Tuscany, Veneto, and Emilia-Romagna, and Public Health Agency of Lazio Region.
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