Breast cancer: T2DM tied to higher odds of TNBC vs ER+/HER2− tumors

  • Chen H & al.
  • Cancer Epidemiol Biomarkers Prev
  • 8 Aug 2019

  • curated by Miriam Davis, PhD
  • Univadis Clinical Summaries
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  • Odds of triple-negative breast cancer (TNBC), rather than estrogen receptor-positive/human epidermal growth factor receptor 2-negative (ER+/HER2) disease, appears greater among women with type 2 diabetes (T2DM), particularly with metformin use.

Why this matters

  • Multiple meta-analyses have established an association between T2DM and breast cancer.
  • This is the first study to examine the relationship by cancer subtype and explore the effect of antidiabetic agents.
  • Findings suggest a need for more frequent breast cancer screening in T2DM.

Study design

  • Retrospective multicenter population-based case-case study of 4557 patients with newly diagnosed breast cancer from 2 Surveillance, Epidemiology, and End Results (SEER) database sites: Seattle, Washington (2004-2015), and Albuquerque, New Mexico (2004-2012).
  • Funding: NIH.

Key results

  • History of T2DM (vs no history) was associated with 38% excess risk for TNBC (aOR, 1.38; 95% CI, 1.01-1.89) vs ER+/HER2 subtype.
  • History of T2DM conferred no excess risk (vs ER+/HER2) for:
    • ER+/HER2+ subtype.
    • HER2 overexpressing (ER/progesterone receptor-negative and HER2+) subtype.
  • Metformin use was only associated with excess risk for TNBC vs ER+/HER2 subtype:
    • Use within 6 months of diagnosis (vs nondiabetic): OR, 1.54; 95% CI, 1.07-2.22.
    • Use within 13-24 months of diagnosis (vs nondiabetic): OR, 1.80; 95% CI, 1.13-2.85.


  • Mostly white population, limiting generalizability.
  • Retrospective, observational design.

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