In Breast Cancer Chemosensitivity, a group of world leading experts review critical aspects of resistance to systemic therapy in breast cancer patients. Beginning with a clinical overview of the problem Breast Cancer Chemosensitivity moves on to focus on the latest findings of molecular mechanisms of drug resistance. These include in-depth discussions on multidrug resistance by P-glycoprotein and the multidrug resistance protein family, resistance to therapeutic agent-induced apoptosis, cell cycle deregulation, deregulation of DNA repair, loss of tumor suppressor genes, integrin-mediated adhesion, insulin-like growth factors, epidermal growth factor, and ErbB2 in modulating breast cancer response to systemic therapy, especially, certain chemotherapeutic agents. Mechanisms of resistance to hormonal therapy are also discussed. Breast Cancer Chemosensitivity provides an example of using novel approaches for chemosensitization of breast cancer cells that gives readers an idea about the future direction in breast cancer treatment.