TNM: principles, history, and relation to other prognostic factors

The TNM classification system describes the anatomic extent of cancer. The ability of TNM to separately classify the individual tumor (T), lymph node (N), and metastatic (M) elements and then group them into stages differs from other cancer staging classifications, which are concerned only with summarized groups. The objectives of TNM classification are to aid the clinician in the planning of treatment, to give some indication of prognosis, to assist in the evaluation of the results of treatment, and to facilitate the exchange of information. The most important challenge facing TNM is how to interface with the great numbers of nonanatomic prognostic factors that are currently in use or under study. As nonanatomic prognostic factors become widely used, TNM provides an inviting foundation upon which to build a prognostic classification; however, there is a risk that TNM will be overwhelmed by such a variety of prognostic data. An anatomic extent of disease classification is needed to select the initial therapeutic approach, stratify patients for therapeutic studies, evaluate nonanatomic prognostic factors at specific anatomic stages, compare the weight of nonanatomic factors with extent of disease, and communicate extent of disease data in a uniform manner. Methods are needed to express overall prognosis without losing the vital anatomic content of TNM. These methods should be able to integrate multiple prognostic factors, including TNM, yet permit TNM to remain intact and distinct.