Introduction
The circadian clock with a 24-hour period is an essential biological and behavioral system that persists in plants, animals, and humans and regulates a variety of processes, including the cell cycle, body temperature, immunity, heartbeat, basal metabolism, blood pressure, hormone secretion, sleep-wake cycle, feeding, and glucose homeostasis (1). The system is coordinated with environmental stimuli such as food intake, light, and temperature (2). In humans, the circadian rhythm consists of two components: the brain clock in the anterior hypothalamus, supra chiasmatic nucleus (SCN), and the peripheral clock in the individual cells (3, 4, 5, 6). The brain clock regulates the peripheral clock of cells and functions as a pacemaker (3, 4, 5, 6). Cellular clocks have autonomous rhythms and answer to intermittent signals from the SCN (3, 4, 5, 6). Additionally, circadian pathway genes control the circadian rhythm (7, 8).
In 1917, 1978, 1997, and 2001, the clock genes were reported for the first time in the fruit fly Drosophila , the fungusNeurospora , the rat, and finally the human, respectively (9). In 2017, the Nobel prize was awarded to scientists who discovered critical molecular mechanisms that control the circadian rhythm (10, 11). The Per (period homolog)1, 2, 3, Clock ,BMall , and Cry (cryptochrome) 1,2 genes and their products constitute a transcription-translation feedback loop (TTFL) associated with the circadian rhythm (12). During the day, Clock and BMall interact to initiate the transcription of the Cry and Per genes (12). TheCry and Per proteins are subsequently linked in the cytoplasm (12). This complex migrates to the nucleus and inhibitsBMall and Cry gene-mediated transcription (12). TheCry-Per complex is destroyed at night, and the cycle begins again (12).
Cancer is a significant cause of death worldwide (13). Cancer incidence has increased due to aging, changes in associated risk factors, and socioeconomic developments (14). Furthermore, some mutations in DNA replication and exogenous or endogenous DNA damage are associated with cancer (15, 16). Several studies showed that disruption in circadian rhythm results in metabolic syndrome, endocrine disorders, and cancer (17). In circadian patterns, individuals are typically classified as morning or evening types (18). Morning types wake up early and function better in the morning (18). Evening types stay up late and perform best at night (18). Dysregulation of circadian rhythms in humans is associated with different cancers such as hepatocellular carcinoma (19), colon (20), ovarian cancers (21), prostate (22), and lung (23). Consequently, the proper function of clock proteins and circadian rhythm plays a crucial role in cancer prevention and treatment (24). In this study, we aimed to assess the circadian rhythm types using MEQ in cancer patients.