The terminology of pre-invasive cervical lesions in the UK cervical screening programme

The terminology of non-invasive epithelial abnormalities associated with an elevated risk of having or developing invasive cervical carcinoma (pre-invasive lesions) has been modified frequently over time as understanding of the underlying biology, and approaches to disease management, have changed. The arguments are now converging on the conclusion that the most appropriate terminology for cervical squamous intraepithelial abnormalities should be two-tier rather than three-tier. Given the findings of the Lower Anogenital Squamous Terminology (LAST) project in the USA, which have recently been endorsed by the World Health Organisation classification of tumours of female reproductive organs, the recommended terms are low-grade and high-grade squamous intraepithelial lesion (SIL), with the option of including the relevant cervical intraepithelial neoplasia (CIN) grade in parentheses. Although, at first sight, this appears to represent only a small change, there is a fundamental conceptual difference between the systems. The CIN system requires, first, the identification of a CIN lesion and, second, the determination of its grade on a continuum, with subsequent division into three grades. The SIL system is based on the existence of two different forms of human papillomavirus (HPV) infection, with productive infection leading to low-grade SIL and transforming infection leading to high-grade SIL.