The research team found that metformin did affect the metabolism of breast cancer cells in people who don’t have diabetes.

They recruited people between 2011 and 2013, and reported the results in 2018.

Results

This study recruited 40 women who were due to have chemotherapy and surgery for newly diagnosed breast cancer.

They took metformin tablets once a day for between 13 and 21 days before they started chemotherapy. They also had a PET-CT scan, blood tests and a biopsy before and after the course of metformin.

The research team found there were two main types of response to metformin.

FDG responders

Just under 8 out 10 people (78%) were what they called FDG responders. FDG is a mildly radioactive marker that doctors use to look at the metabolism of cells on a PET-CT scan.

The scans of people in this group showed the amount of FDG taken up by the cancer cells increased after they took metformin. It’s likely that the metformin caused the cancer cells to change the way their metabolism works.

These patients were also more likely to have a decrease in the level of a particular genetic marker. This suggests their breast cancer cells may grow more slowly after treatment with metformin.

OXPHOS responders

Just over 2 out of 10 people (22%) were what they called OXPHOS responders. This means that there were extra copies of certain genes in the women’s cancer cells after they took metformin.

These OXPHOS genes are involved with part of the cell called the mitochondria and with helping cancer cells grow. Mitochondria produce the energy that cells need to grow and survive. They are sometimes called ‘the energy powerhouses of cells’.

Metformin may be less likely to work on cancer cells which have extra copies of these genes after treatment. In other words, the cells may be resistant to metformin.

Growth of cancer cells

Other studies had shown that metformin can reduce the growth of cancer cells. But the results of this study showed that there wasn’t much change.

They did find that people classed as OXPHOS responders had an increased number of certain genes involved with cell growth. There were less of these genes in some people who were FDG responders.

Conclusion

The research team concluded that it was likely that metformin does change the metabolism of breast cancer cells in some people. They suggest that more trials are done to find out if metformin could be a useful treatment for breast cancer.

Researchers also want to find out whether there are specific genes that could tell us which breast cancer patients are more likely to respond to metformin.