Abstract B100: Rotating night shift work and risk of ovarian cancer

Abstract

Abstract Introduction: Night shift work has been associated with higher risks of breast, endometrial, colorectal, prostate cancer and non-Hodgkin's lymphoma. These associations may be driven by a diminished ability of the pineal gland to produce melatonin among those exposed to light at night. Melatonin likely has multiple anti-cancer mechanisms, including down-regulation of the reproductive axis and direct actions of melatonin on estrogen receptors — both of note for ovarian cancer. Moreover, melatonin exhibits a growth-inhibitory effect on ovarian cancer cell lines. Few epidemiological studies have evaluated an association between night shift work and ovarian cancer risk. Within the NHS and NHSII cohorts, we prospectively assessed the association of rotating night shift work with ovarian cancer risk. Methods: Total number of years of rotating night shift work (defined as at least 3 nights per month in addition to days and evenings during that month) was queried in 1988 for NHS and in 1989 for NHSII. Duration was updated in 1991, 1993, 2001, and 2005 for NHSII. We used Cox proportional hazards regression to model the incidence rate ratios (RR) and 95% confidence intervals (CI) of ovarian cancer for each shift work category (1-2 years, 3-5 years, 6-9 years, 10-14 years, 15-19 years, 20-29 years, and 30+ years), compared to those who never worked rotating shifts, adjusting for age in months, cohort, tubal ligation, duration of oral contraceptive use, parity, BMI, smoking status, menopausal status, family history of ovarian cancer, and duration of breastfeeding. In our analysis, we updated the values for these covariates when new data were available and otherwise carried forward the values from the previous cycle or the last cycle when each covariate was assessed. Results: There were 666 cases of ovarian cancer among 2,856,537 person-years of follow-up time. Overall, rotating shift work was not associated with ovarian cancer risk: 15-19 years vs. none: OR: 1.21; 95% CI: 0.78-1.86; 20-29 years vs. none: OR: 0.65; 95% CI: 0.35-1.19; 30+ years vs. none: OR: 0.79; 95% CI: 0.40-1.54. Estimates were unchanged when adjusted for menstrual irregularity. Conclusion: In this large prospective study, overall, there was no association between duration of rotating night shift work and risk of ovarian cancer. Additional analyses stratifying by hormonal receptor status. menopausal status and other potential effect modifiers are ongoing and may reveal subgroup associations. Citation Information: Cancer Prev Res 2010;3(12 Suppl):B100.