title: Shift work and breast cancer among women textile workers in Shanghai, China.
abstract: OBJECTIVE
  Although night-shift work has been associated with elevated risk of breast cancer in numerous epidemiologic studies, evidence is not consistent. We conducted a nested case-cohort study to investigate a possible association between shift work including a night shift and risk of breast cancer within a large cohort of women textile workers in Shanghai, China.
  
  
  METHODS
  The study included 1,709 incident breast cancer cases and 4,780 non-cases. Data on historical shift work schedules were collected by categorized jobs from the factories, where the study subjects had worked, and then were linked to the complete work histories of each subject. No jobs in the factories involved exclusively night-shift work. Therefore, night shift was evaluated as part of a rotating shift work pattern. Hazard ratios and 95 % confidence intervals were calculated using Cox proportional hazards modeling adapted for the case-cohort design for years of night-shift work and the total number of nights worked. Additionally, analyses were repeated with exposures lagged by 10 and 20 years.
  
  
  RESULTS
  We observed no associations with either years of night-shift work or number of nights worked during the entire employment period, irrespective of lag intervals. Findings from the age-stratified analyses were very similar to those observed for the entire study population.
  
  
  CONCLUSIONS
  The findings from this study provide no evidence to support the hypothesis that shift work increases breast cancer risk. The positive association between shift work and breast cancer observed in Western populations, but not observed in this and other studies of the Chinese population, suggests that the effect of shift work on breast cancer risk may be different in Asian and Caucasian women.
authors.affiliation: Program in Epidemiology, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave. N., Mailbox: M4 A-402, Seattle, WA, 98109, USA, wli@fhcrc.org.
authors.forename: Wenjin
authors.initials: W
authors.lastname: Li
authors.forename: Roberta M
authors.initials: RM
authors.lastname: Ray
authors.forename: David B
authors.initials: DB
authors.lastname: Thomas
authors.forename: Scott
authors.initials: S
authors.lastname: Davis
authors.forename: Michael
authors.initials: M
authors.lastname: Yost
authors.forename: Norman
authors.initials: N
authors.lastname: Breslow
authors.forename: Dao Li
authors.initials: DL
authors.lastname: Gao
authors.forename: E Dawn
authors.initials: ED
authors.lastname: Fitzgibbons
authors.forename: Janice E
authors.initials: JE
authors.lastname: Camp
authors.forename: Eva
authors.initials: E
authors.lastname: Wong
authors.forename: Karen J
authors.initials: KJ
authors.lastname: Wernli
authors.forename: Harvey
authors.initials: H
authors.lastname: Checkoway
mesh_terms: D001943:Breast Neoplasms / Q000453:epidemiology* / Q000209:etiology; D002681:China / Q000453:epidemiology; D015331:Cohort Studies; D005260:Female; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D016273:Occupational Exposure / Q000009:adverse effects*; D012307:Risk Factors; D011795:Surveys and Questionnaires; D013783:Textile Industry; D016387:Women's Health; D014940:Work Schedule Tolerance