Biological clock and cancer

In the present paper, we are giving a review about the circadian rhythm of the biological rhythm, its regulation and relation to tumorigenesis. The circadian rhythm is an approximately 24-hour cycle in biochemical, physiological processes in organisms from unicellular to vertebrates. This biological rhythm is generated by the synchronization of our endogenous clocks and the light as the main “Zeitgeber”. The nucleus suprachiasmaticus (SCN) of the hypothalamus is the region, which is considered to be the circadian “main clock” of the organism and is responsible for coordinating peripheral clocks in different organ systems. At the cellular level, the regulation of the circadian rhythm is basically provided by the so-called “circadian locomotor output cycles kaput” the CLOCK genes. The discovery of those cellular mechanisms was awarded with Nobel Prize in 2017. The CLOCK genes, acting on other effector genes, regulate diurnal rhythm of protein synthesis. More and more data are available, which suggest that there is an association between circadian genes and tumor development. Furthermore, many studies show a link between the shift work and the development of breast and prostate cancer and between mutations in some circadian genes and development of carcinomas. More data suggest a relationship between tumor metabolism and CLOCK genes and their regulations. Based on all these data, the circadian rhythm, so the time of day, may need to be taken into account during cancer therapy.