Abstract B37: Urinary melatonin levels and risk of breast cancer in the Nurses' Health Study II

Abstract

Abstract Shift work has been hypothesized to increase breast cancer risk as two recent meta-analyses suggest a 21- 51% increased risk of breast cancer in women reporting night shift work. Melatonin, a hormone produced by the pineal gland that follows a circadian rhythm with highest levels observed at night, is frequently referenced as the biological mechanism through which shift work may increase breast cancer risk. While decreased urinary melatonin levels are associated with an increased risk of breast cancer in postmenopausal women, only three studies have evaluated the association between melatonin levels and breast cancer in premenopausal women with inconsistent findings. Therefore, we investigated this relationship in predominantly premenopausal women by conducting a nested case-control study in the prospective Nurses' Health Study II cohort. From 1996 to 1999, first morning urine was collected from 29,613 cancer-free participants who were followed through June 2007. Incident breast cancer was confirmed through review of medical records and pathology reports, and potential confounders were reported on biennial questionnaires and a questionnaire administered at urine collection. Concentrations of 6-sulfatoxymelatonin (aMT6s), the major metabolite of melatonin, were available for 603 cases and 798 controls matched for age, menopausal status, ethnicity, fasting status, luteal day of menstrual cycle, and month, year, day, and time of urine collection. We used multivariable conditional logistic regression models to estimate the risk of breast cancer by quartile of urinary aMT6s concentrations, with cutpoints based on values of control participants. We did not observe an association between melatonin levels and risk of breast cancer (odds ratio for highest versus lowest aMT6s quartile: 0.87, 95% confidence interval: 0.57-1.35). Our results were largely unchanged when we examined the relationship between urinary melatonin levels and invasive breast cancer (n=443 cases, odds ratio for highest versus lowest aMT6s quartile: 0.91, 95% CI: 0.54-1.56), in situ breast cancer (n=160 cases, odds ratio for highest versus lowest aMT6s quartile: 1.23, 95% CI: 0.45-3.35), and among women with ER+ tumors (n=398 cases, odds ratio for highest versus lowest aMT6s quartile: 0.77, 95% CI: 0.44-1.34). These prospective data do not provide strong support for a significant association between urinary melatonin levels and breast cancer risk in predominantly premenopausal women. Citation Format: Susan Boyer Brown, Susan E. Hankinson, Eva S. Schernhammer. Urinary melatonin levels and risk of breast cancer in the Nurses' Health Study II. [abstract]. In: Proceedings of the Twelfth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2013 Oct 27-30; National Harbor, MD. Philadelphia (PA): AACR; Can Prev Res 2013;6(11 Suppl): Abstract nr B37.