Example of Distinct but Similar Appearing Code Structures
The tumor (T), node (N), and metastasis (M) system, developed by the International Union against Cancer and first established in US hospital registries by the American Joint Committee on Cancer, is based on site-specific prognostic indicators. It is updated with advances in prognostic knowledge and new approaches to treatment.
A second system, summary staging, codes cancer spread in anatomic terms with respect to the primary site organ. Summary codes classify the disease as in-situ, localized, regional, distant, or unstaged. The code language is the same for every site, and categories do not change with advances in medical science. Summary staging is most widely used by populated-based registries to track screening and early diagnosis in large demographic groups over time. It is not possible to convert all TNM codes to summary staging, and summary staging cannot be converted to TNM codes or AJCC stage groups.
The Surveillance, Epidemiology and End Results (SEER) Program uses a ten-digit site-specific coding scheme for extent of disease (EOD). This coding scheme is designed to collapse into different stage groupings, including the AJCC stage groups an summary stage.
It is possible that more widespread use of TNM staging in medical settings other than cancer programs approved by the Commission on Cancer of the American College of Surgeons, coupled with increased flexibility in computer interpretation of these data, will encourage central registries to adopt the system in the future. In the meantime, because the code schemes measure different aspects of tumor spread for different purposes, and because they cannot be converted readily from one to another, registrars often must code the three measures separately.