RARA and breast cancer: While the RXR-RXR homodimers are the target of 9-cis retinoic acid and synthetic rexinoids, which are also promising agents in the chemoprevention of mammary tumors (Wu et al, 2002; Kong et al, 2005; Kim et al, 2006; Abba et al, 2008; Uray & Brown, 2011), the RXR-RAR heterodimers are the classic mediators of ATRA activity.