Preinvasive Disease

Malignant lesions for most epithelial organs are thought to arise from specific ‘preinvasive neoplastic lesions’. The histopathological characteristics of these lesions have been well described. A number of other terminologies have been used to describe these lesions, including incipient, precancerous, pre-neoplasia, or commonly intraepithelial neoplasia, as well as at times epithelial dysplasia or preinvasive neoplasia.

Cervical Intraepithelial Neoplasia

Cervical intraepithelial neoplasia (CIN) is a histological term that refers to precancerous transformation of squamous cells of the cervical transformation zone. Typically graded as I–III in the United Kingdom, CIN I represents mild dysplasia confined to the basal third of the epithelium, CIN II represents moderate dysplasia confined to the basal two thirds of the epithelium and CIN III represents severe dysplasia involving more than two thirds of the epithelium or even full thickness. Risk factors associated with CIN include: early age of first intercourse, multiple sexual partners, presence of high-risk subtypes of human papillomavirus (HPV), smoking and immunodeficiency (e.g. HIV, transplant patients on immunosuppressant medication).

Classification

The terminology used to classify preinvasive disease of the cervix has been modified to reflect changes in our understanding of underlying biology and disease management. In the United Kingdom, the CIN I–III system has been the standard classification and is still used in the current guidelines for histopathology reporting. However, the World Health Organisation has endorsed the findings of the Lower Anogenital Squamous Terminology (LAST) project and recommends the use of an alternative system, the Bethesda classification, for reporting of low-grade and highgrade squamous intraepithelial lesions (SIL). This is now the most widely used terminology worldwide.

There are important conceptual differences between the two classification systems. The CIN system requires the identification of a lesion followed by determination of its grade on a continuum of CIN I–III. However, the SIL classification is based on the histological changes seen as a result of two different groups of HPV infection, with productive HPV leading to lowgrade SIL (LSIL) and transforming HPV to high-grade SIL (HSIL). Generally, LSIL equates to CIN I and/or HPV-related changes, and HSIL equates to CIN II–III.