| Summary: | Background: In the UK more than 3 million women are screened each year as part of a national screening programme to prevent cervical cancer. Over half of all positive cervical cytology results are reported as 'borderline changes' and 16% of all colposcopy referrals in the NHS cancer screening programme arise from borderline results. As the majority of borderline reports reflect benign changes this results in both considerable overtreatment and a significant burden on the NHS. High-risk strains of the human papillomavirus (HPV) are known to be the causative agent of cancer of the cervix. Aims: To determine if immunocytochemistry for p16 INK4a, a surrogate marker for HPV infection, can identify which borderline cytology results require further investigation, and whether the application of this additional test would be cost-effective. Methods: A prospective observational study in which liquid-based cytology samples from 500 women with borderline changes were reprocessed and immunostained for p161NK4a. The women were followed up via hospital and primary care records for 2.5 years. The costs associated with the additional test were calculated, and balanced against the costs of investigation and treatment, based on an existing protocol for HPV testing. Results: Immunocytochemistry for p16 INK4a showed a Positive Predictive Value (for an outcome of CIN2/moderate dyskaryosis or greater) of 87% and a Negative Predictive Value of 95%. We estimated a cost saving of approximately £28 per sample resulting from fewer colposcopy visits and follow-up cervical cytology. Conclusions: The high positive and negative predictive values demonstrated in this study suggest p16 INK4a immunocytochemistry may be useful as a tool to distinguish those few women with borderline changes who are genuinely in need of further investigation from those who are p161NK4a -negative and can be returned to normal screening programme recall. The introduction of this test could result in considerable cost savings for the NHS, as well as reduced anxiety for women with borderline results.
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