Adjuvant therapy unequivocally provides a significant and prolonged improvement in survival. It is based on the principle that breast cancer is, for many women, a systemic disease at the time of diagnosis with undetectable dormant micrometastases. These micrometastases may develop into clinically relevant metastases years after primary diagnosis. Characteristics of the primary tumor that may predict the risk of metastatic disease in individual women include:
the involvement (and number) of lymph nodes in the axilla
high histological grade of the primary tumor
large tumor size
other biological factors: estrogen receptor (ER), progesterone receptor (PgR) and human epidermal growth factor 2 receptor (HER2) status.