Taking metformin to prevent problems caused by tamoxifen in women with breast cancer

The study wanted to find out if taking the drug metformin (Glucophage) prevents insulin resistance and issues with the womb caused by tamoxifen (Novaldex) in women with breast cancer. The study found that metformin was able to prevent changes in the womb caused by tamoxifen, and also resulted in weight loss and lower levels of insulin resistance.

Tamoxifen is used as a treatment for women with certain types of breast cancer. However, it may have side effects on the womb such as thickening and cancer risk. Another side effect of tamoxifen is that it causes insulin resistance. Insulin is a hormone that controls blood sugar. Metformin is the drug used for people with type 2 diabetes. It works to prevent insulin resistance. Another side effect of metformin is that it works to prevent the womb from growing. Because of these effects, scientists think that taking metformin may prevent some of the negative side effects of tamoxifen in women with breast cancer.

This study consisted of 102 patients, who all had hormone receptor positive breast cancer. All of the women were post-menopausal and had been treated with tamoxifen for an average of 29 weeks. Just over half of the women took metformin for one year, while the other half did not (the control group). Before treatment commenced, the women were tested to see how thick their womb was, what their level of insulin resistance was, and their weight.

The women in the metformin group started with an average womb thickness of 2.5mm. The women in the control group started with an average womb thickness of 2.9mm. After one year of treatment with metformin, the treatment group had and womb thickness of 2.3mm compared to 3.0mm in the control group. 13.3% of patients in the control group had a “very thick” womb, compared to 5.7% of patients in the treatment group. The patients who received metformin also lost more weight and had a lower level of insulin resistance than those in the control group.

The study concluded that in patients treated with tamoxifen for breast cancer, treatment with metformin resulted in less side effects of the womb, greater weight loss, and lower levels of insulin resistance than those who did not take metformin.

This study was small. More studies need to be done to understand the reasons behind these results and test its long term safety, although metformin has been used for a number of years very safely. More results in a larger trial should follow.

Discuss your treatment plan with your doctor.