CLOCK and neoplasm: It is shown that constant lighting leads to the suppression and significant disruption of clock genes expression, which, in accordance with the literature data, aggravates the severance of pathology; on the contrary, constant darkness promotes clock genes expression which creates more favorable conditions for maintaining circadian homeostasis; the presence of synchronization of the circadian characteristics of the tumor and the host organism contributes to the implementation of the antitumor response [76,77,78].