Disturbance of the master circadian clock has been shown to be associated with cancer, and clock genes including the circadian locomotor output cycles kaput genes (CLOCK), basic helix–loop–helix ARNT-like genes (BMAL), period genes (PERs), and cryptochrome genes (CRYs) may influence critical functions in breast cancer etiology [25–29]. The gene discussed is CLOCK; the disease is cancer.