Cadmium is a heavy metal that is found in the environment and enters our body through either dietary sources or cigarette smoke. Heavy metals, like cadmium tend to bioaccumulate and induce toxicities by interacting with organic compounds inside the cell. Recent studies have suggested that cadmium may play a role in breast cancer by activating the estrogen receptor (ER) (Antila1996, Stoica et al. 2000, Martin et al. 2003, Johnson et al. 2003). Data from our lab also suggest that acute exposure of cadmium promotes ER-dependent cell proliferation and induced ER target gene expression (i.e. cyclin D1, Cathepsin D, and c-myc). However the effects of chronic cadmium exposure are unclear and require further investigation. The current focus of this project is to understand how chronic exposure of cadmium affects breast cancer cell growth. To accomplish this, we have established a cadmium-breast cancer cell line (MCF-7 Cd) by maintaining parental ER+ MCF-7 cells in 10-7 M cadmium for over 3 months. By comparing the growth and gene expression patterns of MCF7-Cd and MCF7 cells, we hope to establish an understanding of how chronic cadmium exposure may contribute to the development of breast cancer.