ABSTRACT
Breast cancer is the most common malignancy afflicting women, and the second leading cause of cancer-related death. Current treatment modalities include surgical resection, radiation, endocrine- and chemotherapy and an increasing repertoire of biologically targeted drugs. Fifteen new drugs were approved by the United States Food and Drug administration (FDA) for breast cancer in the last decade. The availability of more effective treatments has led to a decline in mortality from breast cancer in all stages of the disease. However, the biology of breast cancer remains poorly understood and the multiple treatment options also created a pressing need for better strategies for treatment selection. Currently, highly accurate markers to predict prognosis and probability of response to a given therapy on an individual basis are lacking, and routinely used clinicopathologic variables fail to capture the heterogeneity of breast cancer. As a result, many patients are over treated and others may receive suboptimal combination of treatments. Molecular differences in breast cancer probably account for most heterogeneity in clinical outcome. Geneexpression profiling and other high-throughput molecular analytical 298methods are increasingly applied in breast cancer research to comprehensively measure molecular differences in cancers in the hope that a combination of multiple genes will be more informative in predicting disease outcome and response to a specific therapies than any single gene alone. Existing and emerging single and multi-gene tests to personalize treatment selection will be discussed in this chapter.
