title: Breast cancer among nurses: is the intensity of night work related to hormone receptor status?
abstract: The aim of this study was to investigate whether night work is related to breast cancer receptor status. The effect of night work on the risk of estrogen receptor- and progesterone receptor-defined breast cancers was evaluated in 513 nurses diagnosed with breast cancer between 1996 and 2007 and in 757 frequency-matched controls, all of whom were selected from a cohort of Norwegian nurses. Odds ratios for the exposure "duration of work with a minimum of 6 consecutive night shifts" were compared for tumor subgroups with respect to the common control group through the use of polytomous logistic regression. Statistically significant associations were observed between breast cancer and work durations of ≥ 5 years with ≥ 6 consecutive night shifts, with the highest risk observed for progesterone receptor-positive tumors (odds ratio = 2.4, 95% confidence interval: 1.3, 4.3; P-trend = 0.01). When the exposure variable was dichotomized (ever/never worked ≥ 6 consecutive night shifts), a borderline statistically significant heterogeneity (P = 0.05) was seen between progesterone receptor-positive and progesterone receptor-negative tumors in postmenopausal women. The association observed between consecutive night shifts and progesterone receptor-positive cancers suggests that progesterone could play an important role in the detrimental effects of night work.
authors.affiliation: Department of Occupational Medicine and Epidemiology, National Institute of Occupational Health, Pb 8149 Dep, 0033 Oslo, Norway. jasl@stami.no
authors.forename: Jenny-Anne S
authors.initials: JA
authors.lastname: Lie
authors.forename: Helge
authors.initials: H
authors.lastname: Kjuus
authors.forename: Shan
authors.initials: S
authors.lastname: Zienolddiny
authors.forename: Aage
authors.initials: A
authors.lastname: Haugen
authors.forename: Kristina
authors.initials: K
authors.lastname: Kjærheim
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000209:etiology; D016009:Chi-Square Distribution; D005260:Female; D006801:Humans; D007407:Interviews as Topic; D016015:Logistic Models; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D009726:Nurses / Q000706:statistics & numerical data*; D016017:Odds Ratio; D011960:Receptors, Estrogen / Q000502:physiology*; D011980:Receptors, Progesterone / Q000502:physiology*; D012042:Registries; D012307:Risk Factors; D014940:Work Schedule Tolerance / Q000502:physiology*
chemical_list: D011960:Receptors, Estrogen; D011980:Receptors, Progesterone
keywords: Norway; breast cancer; case-control studies; chronobiology phenomenon; estrogen; nurses; progesterone; receptors