CCND1 and breast cancer: For example, Brn-3b drives growth and proliferation in some cells by enhancing the expression of cell cycle proteins such as cyclin D1 and CDK4.19, 20 Accordingly, elevated Brn-3b in solid tumours, such as childhood neuroblastomas and breast cancers, correlates with increased cyclin D1 levels.17, 21, 22, 23 However, if growth-promoting Brn-3b is co-expressed with p53, which inhibits cell growth, such conflicting signals drive apoptosis and under such conditions, Brn-3b interacts and co-operates with p53 to increase transcription of pro-apoptotic Bax, thereby increasing cell death.24