Circadian Disruption Shift Work and Breast Cancer Risk.

Night shift work is designated a probable carcinogen based on epidemiologic studies in humans and mechanistic studies in animals. Increased cancer risk from night shift work is thought to result from the disruption of the normal circadian rhythms from exposure to light at night. Individual cancer risk due to night shift work varies, depending on individual sensitivity of the circadian system to light at night related disruption, pre-existing breast cancer risk, night shift schedules and environmental light at night exposures. Currently, there is no evidence for interventions to minimize or prevent breast cancer risk. Screening at-risk individuals seems appropriate.