MA.32 is a phase III trial set up to assess if the addition of metformin to standard breast cancer treatment improves outcomes in the two most common types of breast cancer, hormone receptor-positive or negative.

Metformin belongs to a class of drugs called biguanides, which are used to treat high blood sugar or diabetes. Previous observational and pre-clinical studies suggested metformin may also reduce the risk of development and increase survival of some cancers, including breast cancer. It was theorized the drug may slow breast cancer growth by improving patient metabolism, notably insulin levels, leading to reduced growth of cancer cells, or that it might impact cancer cells directly.

Results of the MA.32 trial showed that a widely used and inexpensive Type 2 diabetes drug, once hoped to hold enormous promise in treating breast cancer, does not prevent or stop the spread of the most common forms of the disease, according to new findings.

Overall, researchers found the addition of metformin to standard breast cancer treatments did not improve outcomes in the two most common types of breast cancer, hormone receptor-positive or negative.

However, the trial found a potentially important result for individuals with a less common but aggressive form of the disease, called HER2-positive breast cancer.

For this subtype of breast cancer, researchers found there was evidence that use of metformin for five years might lead to a reduction in deaths. HER2-positive cancer makes up about 20 per cent of all breast cancers.

These results need to be replicated in future research before metformin is used as a breast cancer treatment, however, it could provide an additional treatment option for HER2-positive breast cancer.

The above findings were presented by Dr. Goodwin at the 2021 San Antonio Breast Cancer Symposium.

The study is run and sponsored by the Canadian Cancer Trials Group (CCTG) under the umbrella of the Breast International Group (BIG) network.

Pharmaceutical partner: Apotex

Not at present

This research was funded by the Canadian Cancer Society, the National Cancer Institute (US), the Canadian Breast Cancer Foundation, the Breast Cancer Research Foundation, Cancer Research UK, Hold’Em for Life Charity Challenge and Apotex (Canada).

NCT01101438