When breast cancer is diagnosed, it is important to know the stage and grade of the cancer. This helps your doctors decide on the best treatment for you. The stage of a cancer describes its size and whether it has spread from where it started. The grade of a cancer describes how the cancer cells look compared to normal cells and how quickly they grow.
The most common systems to describe the stage of a cancer are number staging and TNM staging:
Number staging describes breast cancer in stages. These go from stage 0 (the cancer cells are in the ducts of the breast) through to stage 4 (the cancer has spread to other parts of the body).
TNM staging looks at the size of the cancer, whether it has spread to the lymph nodes or to other parts of the body.
To grade a breast cancer, a doctor examines a sample of the cancer cells under a microscope. They grade the cells from grades 1–3, or from low-grade to high-grade.