Recent advances have been made in several areas of molecular biology that have improved our understanding of the development and spread of breast cancer. Previous epidemiological studies provided incontrovertible evidence that hormones are crucial determinants of breast cancer susceptibility, and recent discoveries have further defined the interaction of estrogen with its receptors. Additional progress has been made in understanding the role of apoptosis and telomerase expression in breast cancer development and prognosis. Finally, rapid progress continues to be made in the area of breast cancer genetics.