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.