title: Diabetes and breast cancer in Taiwanese women: a detection bias?
abstract: OBJECTIVE
  To evaluate whether diabetes is a risk factor for breast cancer considering confounders and potential detection examinations.
  
  
  METHODS
  National Health Insurance data on 501,747 women without breast cancer were retrieved. Three-year cumulative incidence (2003-2005) and risk ratios (RRs) between diabetic and nondiabetic women were calculated. Potential detection examinations were compared between diabetic and nondiabetic women by chi-square test. Odds ratios (ORs) were estimated by logistic regression for diabetes status/duration with and without adjustment for potential detection examinations and confounders.
  
  
  RESULTS
  The crude RR (95% confidence interval [CI]) for all ages, and age groups < 50, 50-64 and ≥ 65 years, was 2·62 (2·31-2·91), 2·69 (2·11-3·44), 1·39 (1·15-1·68) and 1·37 (1·03-1·84), respectively. Patients with diabetes more frequently received potential detection examinations than nondiabetes (17·5% vs. 7·4%, P-value < 0·001). The unadjusted OR (95% CI) for breast cancer for diabetes status (yes vs. no) was 2·63 (2·31-2·98) and was significant for any diabetes duration. The OR for diabetes status was 1·81 (95% CI: 1·59-2·06) after adjustment for potential detection examinations. In models adjusted for potential detection examinations, age, living region, occupation, comorbidities and used medications, OR for diabetes status attenuated to 1·13 (95% CI 0·96-1·32, P-value = 0·14) and none was significant for any diabetes duration. Potential detection examinations were associated with a fivefold to sevenfold higher risk in various models, indicating a strong impact of detection bias.
  
  
  CONCLUSIONS
  An association between diabetes and breast cancer is observed, but this can be due to potential detection bias and confounders.
authors.affiliation: Department of Internal Medicine, National Taiwan University College of Medicine, Taipei, Taiwan; Division of Endocrinology and Metabolism, Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan; Division of Environmental Health and Occupational Medicine, National Health Research Institutes, Taipei, Taiwan.
authors.forename: Chin-Hsiao
authors.initials: CH
authors.lastname: Tseng
mesh_terms: D000328:Adult; D017677:Age Distribution; D000368:Aged; D001943:Breast Neoplasms / Q000453:epidemiology / Q000209:etiology*; D003924:Diabetes Mellitus, Type 2 / Q000150:complications* / Q000453:epidemiology; D005260:Female; D006801:Humans; D008875:Middle Aged; D012307:Risk Factors; D015983:Selection Bias; D013624:Taiwan / Q000453:epidemiology
keywords: Breast cancer; Taiwan; cumulative incidence; diabetes mellitus; risk ratio