Shift Work Patterns, Chronotype, and Epithelial Ovarian Cancer Risk

Background: Shift work causing circadian disruption is classified as a “probable carcinogen” and may contribute to the pathogenesis of hormone-sensitive cancers. This study investigated shift work exposure in relation to epithelial ovarian cancer (EOC) risk.

Methods: In a population-based case–control study with 496 EOC cases and 906 controls, lifetime occupational histories were collected and used to calculate cumulative years of shift work exposure, average number of night shifts per month, and average number of consecutive night shifts per month. ORs and 95% confidence intervals (CI) for associations with EOC risk were estimated using logistic regression. Associations were also examined according to chronotype and menopausal status.

Results: More than half of the cases (53.4%) and controls (51.7%) worked evening and/or night shifts. There was no clear pattern of increasing EOC risk with increasing years of shift work; the adjusted OR of EOC comparing the highest shift work category versus never working shift work was 1.20 (95% CI, 0.89–1.63). This association was more pronounced among those self-identified as having a “morning” chronotype (OR, 1.64; 95% CI, 1.01–2.65). Associations did not greatly differ by menopausal status.

Conclusions: These results do not strongly demonstrate a relationship between shift work and EOC risk.

Impact: This study collected detailed shift work information and examined shift work patterns according to shift times and schedules. The findings highlight that chronotype should be considered in studies of shift work as an exposure.