The outcome of breast cancer varies widely in patient populations, but is most strongly determined by the following factors; the specific pathology of the primary tumor, whether the tumor is invasive or in situ, the tumor size, and the absence and involvement of lymph nodes. The American Joint Committee on Cancer (AJCC) staging system is used to divide patient disease into five stages (O to IV). The stage of disease progression is strongly correlated to patient survival.
Staging is based on knowledge of the way cancer develops. Some staging systems cover many types of cancer; others focus on a particular type. For most cancers, the stage is based on three main factors:
- Location of the primary (original) tumor
- Tumor size and number of tumors
- Presence or absence of metastasis (whether or not the cancer has spread to distant areas of the body)
In addition, for the classification of the specific breast cancer tumor type according to the AJCC staging criteria, identification of hormone receptor status and presence of HER2 amplification are crucial considerations in the identification and subsequent management of breast cancer.