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External adjustment of unmeasured confounders in a case-control study of benzodiazepine use and cancer risk.

Authors
  • Thygesen, Lau Caspar1
  • Pottegård, Anton2, 3
  • Ersbøll, Annette Kjaer1
  • Friis, Søren4
  • Stürmer, Til5
  • Hallas, Jesper2, 3
  • 1 National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark. , (Denmark)
  • 2 Clinical Pharmacology and Pharmacy, Department of Public Health, University of Southern Denmark, Odense C, Denmark. , (Denmark)
  • 3 Department of Clinical Chemistry & Pharmacology, Odense University Hospital, Odense C, Denmark. , (Denmark)
  • 4 Danish Cancer Society Research Center, Danish Cancer Society, Copenhagen Ø, Denmark. , (Denmark)
  • 5 Department of Epidemiology, Gillings School of Global Public Health, University of North Carolina, Chapel Hill, North Carolina, USA.
Type
Published Article
Journal
British Journal of Clinical Pharmacology
Publisher
Wiley (Blackwell Publishing)
Publication Date
Nov 01, 2017
Volume
83
Issue
11
Pages
2517–2527
Identifiers
DOI: 10.1111/bcp.13342
PMID: 28599067
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

Previous studies have reported diverging results on the association between benzodiazepine use and cancer risk. We investigated this association in a matched case-control study including incident cancer cases during 2002-2009 in the Danish Cancer Registry (n = 94 923) and age- and sex-matched (1:8) population controls (n = 759 334). Long-term benzodiazepine use was defined as ≥500 defined daily doses 1-5 years prior to the index date. We implemented propensity score (PS) calibration using external information on confounders available from a survey of the Danish population. Two PSs were used: The error-prone PS using register-based confounders and the calibrated PS based on both register- and survey-based confounders, retrieved from the Health Interview Survey. Register-based data showed that cancer cases had more diagnoses, higher comorbidity score and more co-medication then population controls. Survey-based data showed lower self-rated health, more self-reported diseases, and more smokers as well as subjects with sedentary lifestyle among benzodiazepine users. By PS calibration, the odds ratio for cancer overall associated with benzodiazepine use decreased from 1.16 to 1.09 (95% confidence interval 1.00-1.19) and for smoking-related cancers from 1.20 to 1.10 (95% confidence interval 1.00-1.21). We conclude that the increased risk observed in the solely register-based study could partly be attributed to unmeasured confounding. © 2017 The British Pharmacological Society.

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