Recent studies strongly support the theory that breast precancers such as atypical hyperplasia (AH) and ductal carcinoma in situ (DCIS) are closely related to the development of invasive breast cancer. There is growing belief that reduction in the burden of breast intraepithelial neoplasia (IEN) through intervention may translate into a decreased burden of invasive cancer. Current research is focusing on two issues. First, improved modalities for detecting precancers are needed; breast epithelial cell analysis appears particularly promising. Second, clinical trials are needed that would permit rapid evaluation of agents that can reduce breast cancer risk. Results of the few available trials suggest that several agents may effectively reduce the burden of breast precancer.