P‐22 P16INK4A AS A MARKER FOR CERVICAL DYSKARYOSIS IN THINPREP® LIQUID BASED CYTOLOGY SAMPLES

Abstract

Cervical cancer is the second most common cancer amongst women worldwide. It is now accepted that almost all cervical cancers arise through the disruption of the pathways of p53 and the product of the retinoblastoma gene (pRb) by high‐risk Human Papilloma Virus (HPV) oncoproteins E6 and E7. In cervical cancer p16INK4a is strongly over expressed when pRb is inactivated by HPV E7. This over expression highlights the potential of p16INK4a as a marker for cervical intraepithelial neoplasia and cervical cancer. Immunocytochemical (ICC) analysis of P16INK4a expression was performed on 30 negative, 30 Borderline, 30 CIN1 and 30 High Grade ThinPrep® cervical samples selected from 1094 consented samples received for routine cervical screening assessment. The results were correlated with HR‐HPV status as determined by a PCR assay and the cytology findings. In addition a real time RT‐PCR technique was employed to evaluate P16INK4a gene expression in 50 of the 120 study samples. Eighty‐five of the 120 cervical samples were found positive by the ICC assay, 13/30 Negative, 23/30 Borderline, 20/30 CIN 1 and 29/30 High Grade. The ICC staining results were supported by the results of the P16INK4a real time RT‐PCR analysis and the HR‐HPV PCR assay. Interestingly not all HR‐HPV positive samples were P16INK4a ICC positive, suggesting the marker may be capable of discriminating between productive viral infections and active cell transformation. In conclusion P16INK4a is a useful marker of HR‐HPV mediated cervical dyskaryosis in ThinPrep® samples and may be utilized as an adjunct to the Pap smear to aid in the identification of patients with lesions which are more likely to progress to cervical cancer. Additional studies correlating p16INK4a ICC with viral load, viral integration and E6/E7 expression are required to establish how discriminatory a marker p16INK4a truly is.