Metformin is supposed to help against cancers. Given that 1 in 8 women get breast cancer, what have the studies shown regarding breast cancer in particular?
I found a great comprehensive article on this point. What did the studies find? The answer was it is mixed.
- Meta-analysis of 7 studies, unknown number of women. “Metformin may have protective effect in postmenopausal women with diabetes. Association stronger with longer metformin use over 3 years.”
- Cohort Study of 68K women. “Diabetic women on metformin had lower incidence of invasive breast cancer. Diabetic women on other antidiabetic drugs had higher incidence.”
- Metanalysis of 12 studies, 16K participants. “No association between Metformin and breast cancer incidence.”
- Metanalysis 11 studies, 838K participants. “Metformin did not reduce breast cancer incidence.”
- Smaller observational studies have shown a positive impact of metformin on breast cancer mortality, especially when used in early stage.
- Metanalysis of 838K patients “Metformin decreased all cause mortality in breast cancer patients.”
- Randomized trial in overweight/obese women at increased risk because of family history or prior atypical breast tissue
- Another personal history of atypical hyperplasia, family history, or high Gail Model Risk
- Those with BRCA. Metformin may inhibit oxidative metabolism to interfere with tumor cell survival.
Patients with diabetes and breast cancer have up to a 50% higher chance of all-cause mortality than those without diabetes.
My thoughts?
There is definitely something here. It makes sense to me as a plastic surgeon and medical professional. When you read about people doing an “anti cancer diet” it is usually anti-inflammatory and LOW SUGAR. So for those women who are pre diabetic or diabetic, metformin is lowering sugar and that may be part of why we see a benefit.
There are limitations to all these studies. What stage of breast cancer? What was their weight? Were they diabetic? Prediabetic? What dosage of Metformin did they take? For how long?
But again, there seems to be a nugget of goodness here. It for sure warrants further study. And given the safety profile of Metformin (most of the issues are GI), particularly if you are high risk for breast cancer and have an elevated Hemoglobin A1c, it deserves a look.