N staging system: tumor-node-metastasis and future perspectives.

The correct staging of disease, with an exact definition of the extent of cancer at the diagnosis, is crucial in the planning of a specific treatment and in the assessment of real chances of cure. Cancer staging systems are expected to be accurate in the description of the severity of a patient's tumor on the basis of the extent of the primary neoplasm and of its spread, thus giving clinician tools to estimate prognosis and providing objective parameters to compare groups of patients in clinical studies. This last point is of wide importance in evaluating successful treatment strategies in oncology, and this is one of the issues that contributed to the development of stage-adapted therapies.