Breast cancer is the most common form of malignancy affecting women worldwide, with approximately 178,480 new cases of invasive breast cancer and 62,030 new cases of in situ breast cancer expected in the United States (US) in 2007. Approximately 40,460 women are expected to die of breast cancer in the coming year, making the disease the second leading cause of cancer-related mortality among women (trailing only cancers of the lung and bronchus). However, thanks in part to recent advances in treatment, mortality rates associated with breast cancer have declined consistently since 1990.