Fig. 1

The two-process model of sleep is mediated by the interaction between a homeostatic process (curve in green) that determines the rise of sleep pressure during the waketime and its fall during sleep and a circadian process (curve in red) that follows a 24-h rhythm driven by the suprachiasmatic nucleus, the master pacemaker. The temporal evolution of homeostatic and circadian processes is most often aligned but can be disturbed particularly in sleep deprived conditions and misalignment (e.g., jet lag, shift work, delayed/advanced clock). As a result, sleep will be misaligned with the circadian rhythm (e.g., rise vs fall in body temperature). It is unclear whether circulating tumor cells (CTCs, blue circles) increased due to sleep or circadian phase. Two hypotheses have been illustrated: A the impact of sleep with elevated CTC levels during sleep increasing in sleep-deprived condition and with separation from the circadian rhythm in the misaligned condition and B the impact of the circadian rhythm with high levels of CTCs during the circadian phase (i.e., fall in body temperature) that do not follow the sleep pattern during sleep deprivation and misaligned conditions. This figure has been modified from Lane et al. [12]. CTCs, circulating tumor cells