Introduction to Summary Staging
The concept of describing disease by stage or extent of disease was introduced in 1929 by the League of Nations' World Health Organization, now known as the World Health Organization, WHO. The first primary site so described was cancer of the cervix.
Staging is a shorthand method for describing disease. A coded format, such as a numerical system with increasing values meaning more involvement or severity, allows electronic analysis of cases with similar characteristics. A simple definition for staging is the grouping of cases into broad categories based on extent of disease.
For cancer, extent of disease is a detailed description of how far the tumor has spread from the organ or site of origin (the primary site). Extent of disease is an anatomic categorization using descriptors to group individual cases in relation to the human body. In other words, extent of disease is an anatomic classification, in which cases are grouped based on specific anatomic criteria. Classification is an orderly arrangement showing relationships among groups.
The relationship between staging, extent of disease, and classification is:
- Extent of disease is a type of classification (based on human anatomy) and pertains to an individual case;
- Staging is coded shorthand or a notation describing disease in more general terms.
By staging, characteristics about a case (precise extent of disease information) can be grouped into categories. Thus staging translates extent of disease classification about individual cancers into groups that can be studied or evaluated for prognostic significance, whereas classification does not necessarily imply a prognosis.
Elements to be considered in any staging system are the primary tumor site, tumor size, multiplicity (number of tumors), depth of invasion and extension to regional or distant tissues, involvement of regional lymph nodes and distant metastases.