CLOCK and cancer: Additional studies have shown that expression of key circadian clock genes are under the control of cGMP (Golombek, et al. 2004; Oster, et al. et al. 2003; Plano, et al. et al. 2012), and that disruption of the normal expression of these genes can result in the development of cancers, including breast cancer (Fu, et al. 2011; Fu and Lee 2003; Gery and Koeffler 2010; Hoffman et al. 2010a,b).