Staging

Distinct from the grading scale that estimates a cancer's aggressiveness, staging estimates how much and where the cancer is located. Several classifications exist but most common is TNM. For most cancers, the stage is based on 3 main factors called the TNM method.

1. T-refers to the original (primary) tumor's size and whether or not the tumor has grown into other nearby areas.
2. N - refers to whether or not the cancer has spread to the nearby lymph nodes.
3. M-whether or not the cancer has spread to distant areas of the body.
   

The numbers are often translated into different stages including: in situ-abnormal but not invasive, and stages I, II, III, IV with subcategories. Usually the higher the number the more advanced the disease. Not all cancers are staged by the TNM method. For e.g., leukemias, are generally not staged in this way because they are already in the blood. Also, primary brain cancers that originate in the brain (primary cancers), tend to be localized and they are graded rather than staged.