Breast cancer is not a single disease. Genetic array tools can define several subtypes. Specific biological processes and distinct gene pathways are associated with prognosis and sensitivity to chemotherapy and targeted agents in different subtypes of breast cancers. As a consequence, breast cancer can be classified by molecular events. A primary challenge for future drug development in breast cancer will be to distinguish genes and pathways that "drive" cancer proliferation (drivers) from genes and pathways that have no role in the development of cancer (passengers). The identification of functional pathways that are enriched for mutated genes will select sub-population of patients the will most likely be sensitive to biology driven targeted agents. The selection of driver pathways in resistant tumors will permit to discover a biology-driven platform for new drug development to overcome resistance. Any of the breast cancer subtypes implies that clinicians should consider cases within the various distinct sub-population in order to properly choose the most personalized therapeutic approach. We will review all new emerging agents targeting the driver pathways within breast cancer molecular subtypes.
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