Circadian disruption and fatal ovarian cancer.

BACKGROUND

The International Agency for Research on Cancer determination that shift work is a "probable" human carcinogen was based primarily on studies of breast cancer but it was also noted that additional aspects of circadian disruption and other cancer sites deserved further research.

PURPOSE

To examine possible associations of three measures of circadian disruption: nontypical work schedules, nightly sleep duration, and monthly frequency of insomnia with risk of fatal ovarian cancer in a sample of American women.

METHODS

Several measures of circadian disruption and other information were assessed in 1982 from 161,004 employed women in the American Cancer Society's Cancer Prevention Study-II, a cohort that has been followed for mortality through 2010. In 2013, Cox proportional hazards regression was used to model the relative risks (RRs) and 95% CIs of death from ovarian cancer for categories of each indicator of circadian disruption.

RESULTS

Over 28 years of follow-up, 1289 deaths from ovarian cancer occurred in the at-risk cohort. Compared to fixed daytime work, a rotating schedule was associated with an elevated risk of fatal ovarian cancer (RR=1.27, 95% CI=1.03, 1.56). No significant associations were observed for sleep duration (p trend=0.24) or insomnia (p trend=0.44).

CONCLUSIONS

In this large prospective study, there was a higher risk of fatal ovarian cancer in women who reported a rotating work schedule. These findings and the high prevalence of rotating shift schedules underscore the need for further research examining the role of work schedule and risk of ovarian cancer.