title: Impact of comorbidity on risk of venous thromboembolism in patients with breast cancer: a Danish population-based cohort study.
abstract: OBJECTIVE
  To assess the interaction between comorbidity and breast cancer (BC) on the rate of venous thromboembolism (VTE) beyond what can be explained by the independent effects of BC and comorbidity.
  
  
  METHODS
  Population-based matched cohort study.
  
  
  METHODS
  Denmark.
  
  
  METHODS
  Danish patients with BC (n=62 376) diagnosed in 1995-2010 and a comparison cohort of women without BC (n=304 803) from the general population were matched to the patients with BC on year of birth in 5-year intervals and on the specific diseases included in the Charlson Comorbidity Index (CCI) and atrial fibrillation and obesity.
  
  
  METHODS
  The rate ratios of VTE per 1000 person-years (PY) were computed by comorbidity levels using the CCI, and interaction contrasts (IC) were calculated as a measure of the excess or deficit VTE rate not explained by the independent effects of BC and comorbidity.
  
  
  RESULTS
  Among patients with BC with a CCI score of 1, the 0-1 year VTE rate was 12/1000 PY, and interaction accounted for 10% of the rate (IC=3.2, 95% CI 0.5 to 5.9). Among patients with BC with CCI ≥4, the VTE rate was 17, and interaction accounted for 8% of the rate (IC=1.2, 95% CI -1.8 to 4.2). There was no interaction during 2-5 years of follow-up.
  
  
  CONCLUSIONS
  There was only little interaction between BC and the CCI score on the rate of VTE.
authors.affiliation: Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Anne Gulbech
authors.initials: AG
authors.lastname: Ording
authors.affiliation: Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Erzsébet
authors.initials: E
authors.lastname: Horváth-Puhó
authors.affiliation: Breast Clinic, Aalborg University Hospital, Aalborg, Denmark.
authors.forename: Jens Peter
authors.initials: JP
authors.lastname: Garne
authors.affiliation: Department of Oncology, Uppsala University Hospital, Uppsala, Sweden.
authors.forename: Petra Witt
authors.initials: PW
authors.lastname: Nyström
authors.affiliation: Institute of Pathology, Aalborg University Hospital, Aalborg, Denmark.
authors.forename: Mogens
authors.initials: M
authors.lastname: Vyberg
authors.affiliation: Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Henrik Toft
authors.initials: HT
authors.lastname: Sørensen
authors.affiliation: Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark Department of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, Georgia, USA.
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Lash
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000150:complications*; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003718:Denmark; D005260:Female; D006801:Humans; D007223:Infant; D008875:Middle Aged; D018570:Risk Assessment; D054556:Venous Thromboembolism / Q000453:epidemiology* / Q000209:etiology*; D055815:Young Adult
keywords: Epidemiology; Oncology