Evaluation of p16INK4a expression in ThinPrep cervical specimens with the CINtec p16INK4a assay: correlation with biopsy follow-up results

BACKGROUND: The aim of this study was to examine p16(INK4a) protein expression in ThinPrep (Cytyc Corporation, Marlborough, Mass) cervical specimens by using the CINtec p16(INK4a) Cytology Kit (Dako, Glostrup, Denmark). The ability of this assay to accurately identify underlying high-grade lesions was assessed by using follow-up biopsies and comparing these results with Hybrid Capture 2 (Digene, Gaithersburg, Md) high-risk HPV (hc(2)) results. METHODS: Three hundred ninety-eight residual ThinPrep samples were collected, and histological follow-up data were retrieved for abnormal cytology specimens. After preparation of a Papanicolaou-stained slide, a second slide was processed in preparation for p16(INK4a) immunostaining. High-risk human papillomavirus testing (hc(2)) was also performed. RESULTS: Of the 163 cytologically abnormal samples, 6-month biopsy follow-up data were available for 45% of the specimens. At initial blinded evaluation, 21 of the 26 cases with cervical intraepithelial neoplasia (CIN) II/III follow-up were positive for p16(INK4a), yielding an overall diagnostic sensitivity of 81%; 29 of the 47 cases diagnosed as CIN I or less were p16(INK4a) negative, yielding a diagnostic specificity of 62%. In comparison, the hc(2) test results indicated a diagnostic sensitivity of 100% with a diagnostic specificity of 15%. After review of selected cases with CIN II/III follow-up, 25 of 26 slides were deemed to be positive for p16(INK4a), increasing the diagnostic sensitivity to 96%. CONCLUSIONS: The CINtec p16(INK4a) Cytology Kit, in combination with ThinPrep cervical samples, allowed clear evaluation of p16(INK4a) protein overexpression. Diagnostic specificity of the CINtec p16(INK4a) assay was significantly improved relative to hc(2). To increase p16(INK4a) immunostaining in abnormal cells, a modified kit version with improved staining performance has been developed and is currently being evaluated.