ABSTRACT Breast cancer is the most common cancer in women, the second most common cause of cancer death in women, and the main cause of death in women aged 40-59. Important risk factors are age, gender, reproductive history, hormonal factors, and family history. Diagnostic evaluation includes screening and diagnostic breast imaging and breast biopsy. There are several histologic kinds of breast cancer; however, 70%–80% of breast cancers are inltrating ductal carcinomas. An assay of hormone receptors is important for both prognostic and predictive purposes as patients could benet from endocrine treatments. Also, HER 2/neu expression should be assayed as it represents an important predictive factor because patients might benet from treatments such as trastuzumab. Other prognostic factors include the status of the draining axillary lymph nodes, tumor size, tumor grade, markers of an elevated proliferative rate, and circulating tumor cells. Treatment of locoregional disease includes surgery, radiation therapy, or both, and treatment of systemic disease with unique or a combination of chemotherapy, endocrine therapy, or biologic therapy. In patients with clinically nodenegative breast cancer, sentinel lymph node biopsy identies the status of the axillary nodes. Primary tumor size, lymph node status, and histologic grade of differentiation are all important prognostic factors to help in the determination of an individual adjuvant systemic therapy.