Staging tests determine the size and location of your cancer and whether it has spread. They also help with treatment planning. Cancer is staged using the numbers 0 through IV.
Stage 0 cancers are also called noninvasive, or in situ (in one place), cancers. Although they don't have the ability to invade normal breast tissue or spread to other parts of your body, it's important to have them removed because they eventually can become invasive cancers.
Stage I to IV cancers are invasive tumors that have the ability to invade normal breast tissue or spread to other areas. A stage I cancer is small and well localized and has a high cure rate. But the higher the stage number, the lower the chances of cure. By stage IV, the cancer has spread beyond your breast to other organs, such as your bones, lungs or liver. Although it's not possible to cure cancer at this stage, it may still respond well to various treatments, which could effectively shrink and control the cancer for an extended period of time.