Evaluation of p16INK4a expression in ThinPrep cervical specimens with the CINtec p16INK4a assay

Abstract

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 (hc₂) 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 (hc₂) 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 hc₂ 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 hc₂. To increase p16^INK4a immunostaining in abnormal cells, a modified kit version with improved staining performance has been developed and is currently being evaluated. Cancer (Cancer Cytopathol) 2007. © 2007 American Cancer Society.