Does Diabetes Treatment (Metformin) Aid Breast Cancer Survival?

Once again, the early hype about a possible new cancer treatment has been proven wrong. As you may know, metformin is a drug used to treat type 2 diabetes. In this kind of diabetes, the insulin naturally produced by the pancreas is not able to get the needed sugar to the cells of the body. Metformin reduces the amount of sugar that the body produces and absorbs and lowers blood sugar levels.

The suggestion that sugar fuels or causes cancer is an enormous over-simplification of complicated biology.

Several observational studies noted that breast cancer patients who were also taking metformin, because they had type 2 diabetes, had improved survival rates. This led to trials for non-diabetic cancer patients that added the drug to established therapies. Already found to not be useful in two lung cancer trials, the latest large breast cancer trial also found it had no impact on survival.

This Canadian study included 3,649 patients with estrogen receptor (ER) positive and/or ER-negative breast cancers and who did not have diabetes. Once again, metformin had no impact on survival. The researchers, in announcing the results, also stated that any off-label use of metformin in the treatment of breast cancer should be halted.

They also commented that diabetic breast cancer patients had not been included in the study, and that the results did not apply to them. If metformin was useful in control of their diabetes, it should not be changed.

This study and the results may not seem so important, but I think that there are related issues that can be considered. We have all heard the suggestions that sugar causes cancer. There have not been any randomized controlled trials to support this belief. Of course, there is a link (indirectly) between sugar and cancer, but it is related to calories.

Many foods that contain a lot of sugar—think cakes and candies or popular beverages—are high calorie and may cause weight gain. We know that estrogen resides in fat cells, and this is the link between excess body weight/BMI and breast cancer risk.

The suggestion that sugar fuels or causes cancer is an enormous over-simplification of complicated biology. Our bodies need glucose. Every single cell in our bodies needs energy to do its job, and the fuel for that energy is glucose. The best guess of the origin of this myth is that cancer cells grow quickly and, therefore, need lots of glucose. The idea, then, would be that starving cancer cells of their fuel might prevent or slow growth.

The catch is that every other cell needs it, too, and there is no way to direct where a glucose molecule goes. Beyond this statement, the science quickly becomes extremely complicated, but the bottom line is that there is no direct link between a chocolate chip cookie or an ice cream cone and cancer.

Like everything else, the key is moderation, but primarily because of calorie and weight concerns. Since obesity brings a high risk of diabetes, and since metformin is useful for diabetes, one can appreciate the thinking that it might possibly fight cancer. Unfortunately, that turns out to be wrong.

The second issue is the reminder of how quickly a new treatment can be touted and advertised, and how often, the positive anticipation is premature. We have all seen the headlines that proclaim: Cancer will be cured by 2040, or other dates that are long past.

We recall President Nixon’s War on Cancer and President Biden’s Cancer Moonshot with the goal of reducing the incidence of cancer by 50%. How wonderful it would be if that could happen! However, I sadly remind us all that cancer is a stealthy and powerful opponent, and that the science is incredibly complex. We advance baby step by baby step.

When you read or hear something that sounds too good to be true, remember that it likely is. Have faith in science and medicine, and listen to the hyperbolic promises with skepticism.