Prostate Cancer Risk Decreases Following Cessation of Night Shift Work

Night shift work has been associated with breast and prostate cancer. Recent studies on breast cancer indicate that risk is highest in women with current night-shift work and decreases with time since last night-shift work. We re-analysed data from the MCC-Spain population based case-control study to evaluate whether the attenuation shown for breast cancer by time since last exposure is also observed in prostate cancer. Incident histologically confirmed prostate cancer cases (n=1093) aged 27-85 were recruited in 11 hospitals in 7 Spanish regions 2008-2013 and were matched to a random sample of general population controls (n=1387). We recorded detailed information on shift work for all jobs and on lifestyle and sociodemographic factors. Subjects with current or recent night shift work (0-2 years) had an Odds Ratio of 1.25 (95%CI 0.86,1.80) compared to never night shift workers. A similar risk was observed for night shift workers who interrupted such an exposure less than 20 years ago (OR=1.23, 0.95,1.60). At 20 years since last exposure, there was no increased risk (OR=1.02, 0.8-1.3, p-value for trend=0.08). The pattern was similar when adjusting also for cumulative duration of night shift work. We describe a pattern of time-related decrease in prostate cancer risk following night shift work with a nearly null association 20 years after last exposure that has also been observed for breast cancer. This pattern may help understand mechanisms of disease and may also explain differences between findings of epidemiological studies.