"Retinoids, or vitamin A analogs, are among the most promising chemopreventive agents for breast cancer (Table I). Two classes of retinoid receptors, RARand RXR, bind retinoids and mediate transcriptional regulation of genes that control cellular proliferation, differentiation, and apoptosis (52). RXR is able to interact with many other factors such as vitamin D receptor (VDR), peroxisome proliferator- activator receptor (PPAR), thyroid hormone receptor, and COUP (Fig. 1). Retinoids have been shown to inhibit the growth and invasiveness of breast cancer cells in vitro and in vivo ("