Could the amount of light, the time of day, or the season of the year affect cancer development and/or best possible time of treatment? The answer may lie in the study of circadian rhythms and chronobiology. The fact that some regulatory hormones are influenced by circadian rhythms may be critically important to cancer screening and chemotherapy administration.
The hormone melatonin, produced by the pineal gland in the brain and secreted at a rate that is suppressed by exposure to environmental lighting, is frequently cited as the key circadian hormone and one that is important in chronobiology. Its role in cancer is quite different: Melatonin may act as an antioxidant that can scavenge free radicals and protect against DNA damage, and it regulates hormonal processes such as estrogen homeostasis. In patients undergoing chemotherapy, free radicals are thought to be a major source of toxicity, and in vitro, melatonin has been shown to reduce chemotherapy toxicity as well as promote apoptotic cell death.