Stage is a classification system used to define the extent of the disease.
In addition to serving as a predictor for the probability of curing the disease, stage is also of critical importance in determining an individual's breast cancer treatment. Physicians often define the stage of an individual's breast cancer according to a clinical staging system and a pathological staging system. Clinical stage refers to the stage of disease as determined by non-surgical means. Pathological stage describes the measurements of the tumor and a microscopic examination of the lymph nodes performed after surgery has removed the tumor.