There are many systems in use in different parts of the world for classifying and naming precancerous conditions of the cervix, based on cytology and histology (see table below). The more useful classification systems incorporate information about the disease's natural history, which has been acquired over the past few decades.

Table

Cervical pre-cancer: terminology for cytological and histological reporting.

The cervical intraepithelial neoplasia (CIN) classification system evolved in 1968, to take into account the different natural histories seen with different degrees of dysplasia (ranging from CIN1/mild, to CIN2/moderate, and CIN3/severe dysplasia). The CIN classification is still used in many countries for cytological reports, although strictly speaking it should only be used for histological reports (i.e. results of microscopic examination of tissue samples).

The Bethesda System was developed in the 1990s at the United States National Cancer Institute. In this system, which should be used only for cytological reports (i.e. results of microscopic examination of a smear), CIN2 and CIN3 are combined into one group, termed high-grade squamous intraepithelial lesions (HSIL), because cytologically it is difficult, if not impossible, to distinguish CIN2 from CIN3. Meanwhile, CIN1 results are termed low-grade squamous intraepithelial lesions (LSIL). In the 2001 Bethesda System, atypical cells are divided into ASCUS (atypical squamous cells of undetermined significance) and ASC-H (atypical squamous cells: cannot exclude a high-grade squamous intraepithelial lesion). This classification is recommended by WHO for cytological reports (see Annex 5).

The International Classification of Diseases (ICD) is the international standard for coding causes of illness and death. In its current 10^th revision it is used in some 110 countries.

The ICD coding scheme for cervical dysplasias and neoplasias follows the WHO scheme as shown in the right-hand column of the table. References to both CIN and HSIL/LSIL are included in the ICD.³ For cancer registration and in order to describe the tissue changes in more detail (histopathology), an adaptation of the ICD has been formulated: the ICD for Oncology (ICD-O). It contains detailed codes for the site of the neoplasia, and an additional set of codes for the histopathology.⁴

The ICD-O classification of the neoplastic tissue types, based on histopathology or tumour morphology, is informed by the work of the International Agency for Research on Cancer (IARC), which is regularly published in the WHO/IARC Classification of Tumours series.⁵ For cervical tumours and dysplasias, the fourth edition of WHO classification of tumours of female reproductive organs was published at the end of March 2014.⁶

The clinical path for treatment and the prognosis depend on the histopathology and the extent of the spread, or stage, of cancer. The Union for International Cancer Control (UICC) TNM classification of malignant tumours is a system based on description of the spread and size of the cancer. It documents the size of the tumour (T), affected lymph nodes (N) and distant metastases (M). The TNM stages are based either on clinical description or on pathological classification (pTNM).⁷ The TNM classification system is compatible with the clinical classification that is produced by the International Federation of Gynecology and Obstetrics (FIGO)⁸ (see Chapter 6, section 6.3).