Diabetes drug may lower risk of certain types of breast cancer



Women with type 2 diabetes (T2D) may have a higher risk of breast cancer either directly due to T2D-associated metabolic dysfunction or indirectly due to risk factors shared by the two diseases. Early studies reported an association between T2D and breast cancer, but many women with T2D take the diabetes drug metformin, which may reduce cancer risk. Thus, it is difficult to disentangle these potentially opposite effects.


IRP researchers led by Dale P. Sandler, Ph.D., examined comprehensive questionnaire and clinical data from 44,541 women participating in the Sister Study, a national cohort of women with a sister who had breast cancer. They determined that while T2D may increase risk of developing breast cancer, the use of metformin appears to prevent this elevated risk, at least for estrogen receptor-positive breast cancer. However, women with T2D treated with metformin were more likely to develop estrogen receptor-negative and triple-negative breast cancer than women without T2D.


Understanding how T2D and the medications used to treat it affect the risk for breast cancer could help doctors identify women who are at an increased risk of developing breast cancer. These women may benefit from additional screening for the disease to catch it in its early stages, when it is most treatable.


Park YM, Bookwalter DB, O'Brien KM, Jackson CL, Weinberg CR, Sandler DP. (2021). A prospective study of type 2 diabetes, metformin use, and risk of breast cancer. Ann Oncol. Mar;32(3):351-359. doi: 10.1016/j.annonc.2020.12.008.

Sandler DP, Hodgson ME, Deming-Halverson SL, Juras PS, D’Aloisio AD, Suarez L, Kleeberger C, Shore DL, Bilhorn A, DeRoo LA, Taylor JA, Weinberg CR for the Sister Study team. (2017). The Sister Study: Baseline methods and participant characteristics. Environ Health Perspect. Mar; 125:127003. doi: 10.1016/j.annonc.2020.12.008.

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This page was last updated on Thursday, June 8, 2023