Circadian clocks are endogenous molecular time-keeping systems that underlie daily fluctuations in multiple physiological and biochemical processes. It is now well recognized that dysfunction of the circadian system may be associated with a heightened incidence of cancer. This brief review presents evidence supporting the important role played by circadian clocks in the development of cancer and the therapeutic efficacy of anticancer agents. A number of circadian clock genes have been identified, which include transcription factors that regulate gene expression. Continued research in this area should increase understanding of the role of circadian clocks which could, ultimately, reduce the incidence of cancer in people with disrupted sleep-wake cycles, such as 24-h shift workers and flight attendants, and provide optimal chronopharmacology for cancer treatment.
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