The role of cancer staging in evidence-based medicine.

The classification of disease is a fundamental aspect of scientific medicine. Only when a specific condition has been recognized and characterized, can we start to acquire knowledge about it. Anatomic staging is a key element in the classification of malignant disease. The effectiveness of cancer treatment is almost always studied in groups of cases defined by stage. Clinical trials, therefore, create knowledge which is largely specific to particular stages of particular cancers. That knowledge can only be used to guide the practice of oncology if patients are staged. Staging the individual case permits the knowledge derived from previous experience to be used to guide the choice of treatment. The routine use of staging in a population also permits knowledge to be used to optimize the effectiveness of cancer control programs.