Use of metformin and survival of diabetic women with breast cancer

Curr Drug Saf. 2013 Nov;8(5):357-63. doi: 10.2174/15680266113136660069.


Objective: This study was set out to determine whether metformin use influences survival in breast cancer patients treated with antidiabetic drugs as compared to non-users.

Research design and methods: We used data from the Danish national registries (1996-2008) to identify adult female patients diagnosed with breast cancer who were prescribed antidiabetic medication. We performed multivariate Coxproportional hazard regression to assess all-cause and breast cancer-specific mortality risks associated with metformin exposure. In a secondary analysis, we stratified use of metformin according to the cumulative number of prescriptions.

Results: Of the 1058 breast cancer patients 349 died during follow-up, with breast cancer listed as the primary cause of death for 152 cases. Compared to non-use, current metformin treatment was associated with a significant reduction in overall mortality (adjusted HR 0.74, 95% CI, 0.58-0.96). For breast cancer-specific mortality, a non-significant risk reduction (adjusted HR 0.88, 95% CI, 0.59-1.29) was observed, which became significant after stratification according to cumulative number of prescriptions. An increased risk of both overall and breast cancer-specific mortality was observed in the first 12 months after discontinuation of metformin.

Conclusions: We observed a nonsignificant reduction in breast cancer-specific mortality associated with metformin exposure among breast cancer patients treated with antidiabetic drugs. However, our findings suggest that long-term metformin use may have a beneficial effect on survival in patients with breast cancer. Further confirmation of these findings is needed.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Breast Neoplasms / complications
  • Breast Neoplasms / mortality
  • Breast Neoplasms / therapy*
  • Cohort Studies
  • Comorbidity
  • Denmark / epidemiology
  • Diabetes Mellitus / drug therapy*
  • Female
  • Follow-Up Studies
  • Humans
  • Hypoglycemic Agents / therapeutic use*
  • Metformin / therapeutic use*
  • Middle Aged
  • Registries
  • Risk Factors
  • Survival
  • Treatment Outcome
  • Young Adult


  • Hypoglycemic Agents
  • Metformin