Long-term survival of patients with breast cancer treated by operation alone has not improved despite many variations in local or regional treatment. Undetectable micrometastases present at the time of initial local treatment are the cause for later failures. Adjuvant systemic treatments have been introduced in the hope of reducing recurrence and mortality. In a series of protocols, the National Surgical Adjuvant Breast Project evaluated sequentially escalating drug therapies and noted a striking change in the natural history of the disease. Breast cancer is a heterogeneous group of diseases with different outcomes. Many of the therapies provide appreciably prolonged disease-free survival and ultimate survival for subsets of patients. Efforts should be made to recruit patients for further clinical trials in order to define better the most suitable treatments for the different subsets of patients.