Breast cancer is the most common invasive cancer in women and the second leading cause of cancer death in women after lung cancer. Advances in screening and treatment for breast cancer have improved survival rates dramatically since 1989. The chance of any woman dying from breast cancer is around 1 in 38 (2.6%).

A doctor stages cancer according to the size of the tumor and whether it has spread to lymph nodes or other parts of the body.

There are different ways of staging breast cancer. One way is from stage 0–4, with subdivided categories at each numbered stage. Descriptions of the four main stages are listed below, though the specific sub stage of a cancer may also depend on other specific characteristics of the tumor, such as HER2 receptor status.

Stage 0: Known as ductal carcinoma in situ (DCIS), the cells are limited to within the ducts and have not invaded surrounding tissues.

Stage 1: At this stage, the tumor measures up to 2 centimeters (cm) across. It has not affected any lymph nodes, or there are small groups of cancer cells in the lymph nodes.

Stage 2: The tumor is 2 cm across, and it has started to spread to nearby nodes, or is 2–5 cm across and has not spread to the lymph nodes.

Stage 3: The tumor is up to 5 cm across, and it has spread to several lymph nodes or the tumor is larger than 5 cm and has spread to a few lymph nodes.

Stage 4: The cancer has spread to distant organs, most often the bones, liver, brain, or lungs.