The TNM system is a method of classifying tumours based on the size of the primary tumour (T), the number of lymph nodes which contain cancer cells (N), and whether or not the cancer has spread or metastasised (M).

The combination of scores for TNM will tell the doctor which stage the cancer is at. It is important to remember that a cancer’s stage does not change, even if the cancer gets worse – stage always refers to the characteristics of the cancer when is was diagnosed. The TNM staging system is used to stage most cancers.