Background In 2007, the International Agency for Research on Cancer classified ”shift work leading to a disruption of circadian rhythm” as probably carcinogenic to humans based on sufficient evidence from experimental animal models but limited evidence from epidemiological studies in humans. In this context, we investigated the role of night shift work in prostate cancer based on data from the EPICAP study.

Methods EPICAP is a French population-based case-control study including 819 incident prostate cancer cases and 879 frequency matched controls. Cases and controls were face-to-face interviewed on their lifetime occupational history with details on work schedules for each job held for ≥6 months. Night work was defined as having performed permanent or rotating night shifts for at least 270 hours/year or 3 nights/month during ≥1 year.

Results Permanent and rotating night work were not associated with prostate cancer (OR=0.99 [0.78–1.26], OR=0.89 [0.66–1.20], respectively]). However, permanent night work was associated with aggressive prostate cancer (OR=1.40 [0.97–2.03]), especially for a duration greater than 25 years (1.89 [1.15–3.11]). Interestingly, an association between night work and prostate cancer risk was observed for men with an evening chronotype (OR=1.82 [1.01–3.28]), especially for rotating night work (OR=2.34 [1.02–5.35]).

Conclusion Our results suggest that night work may be associated with prostate cancer, particularly in men with aggressive prostate cancer or with an evening chronotype. Further investigations are needed to confirm our findings and to take into account a potential influence of an individual susceptibility to circadian genes in this association.