Can metformin help patients in early stage breast cancer? The short answer is likely yes, particularly those who are diabetic or HER2 positive.
It is thought to work by reducing cancer cell proliferation, decreasing signaling in breast cancer tissue, improving immune function. When reading these studies, they go into exactly how (reducing the cellular expression of Ki-67 in breast cancer tissue, suppressing PI3K and RAS/MAPK signaling in breast cancer tissue, etc) but I found that hard to read, so I won’t try to blog about it.
They then quoted studies where metformin was used with chemotherapy
- Landmark study: diabetic patients with breast cancer getting metformin had higher probability of having complete response pathologically, and did better than non diabetic patients who did not take metformin.
- METTEN trial: randomized multicenter trail. Metformin vs. placebo for 24 weeks in nondiabetic patients. Results were inconclusive, but Metformin was shown to decrease the residual breast cancer cell proliferation. This means it may help those with residual disease lower recurrence.
- Study: Metformin used in diabetic patients with triple negative breast cancer. No significant impact of the drug. BUT those who did NOT get Metformin tended to have higher risk of distant metastases, (though it did not lower cancer specific mortality.)
- ALTTO trial: HER2 + breast cancer showed a positive effect of Metformin for disease free survival and distant disease free survival.
- NCIC MA32 study: Metformin used in nondiabetic women at 850mg twice a day. After six months, they had Metformin related improvement in weight, BMI, and metabolic values. They also found HER2+ had benefits in invasive disease free survival.
Conclusions?
It isn’t black and white. It does seem to be that there is *something* here, particularly for women who are diabetic with breast cancer or HER2+. Given the low side effects (nausea, diarrhea) it is likely something to add in if you can, as it seems to prolong disease free survival. Again, the picture is muddy, and I am a plastic surgeon, not an internist or oncologist. With all of these studies, they will hone it more.