CLOCK and obstructive sleep apnea syndrome: Intermittent hypoxia mimicking sleep apnea has been shown to increase HIF-1α in cultured colorectal cancer cells [110], and it seems feasible that OSA might cause both environmental circadian disruption (frequent arousal during sleep) and molecular circadian disruption (activation of HIF-1α, which can alter the molecular clock), which may negatively affect cancer outcomes.