Chen L et al. - Metformin has been reported to lower the risk of incident breast cancer, but it is unclear if metformin affects malignant progression. In the current study it was shown that unlike sulfonylureas and insulin, metformin decreased second breast cancer events (SBCEs).

Methods

• A retrospective cohort study was conducted using the SEER-Medicare database.
• Participants were 66-80 years of age with newly diagnosed with stage I or II breast cancer.

Results

• Among 14,766 women, 791 had SBCEs, 627 had recurrences, and 237 died from breast cancer.
• Use of metformin (n=2558) was associated with 28%, 31%, and 49% lower risks of a SBCE, breast cancer recurrence, and breast cancer death, respectively.
• Use of sulfonylureas or insulin was associated with 1.49- and 2.58-fold higher risks of breast cancer death.