So far, observational studies have suggested a lower risk of cancers, including breast cancer, and better response to chemotherapy in patients with diabetes who are treated with metformin, she said. Results of basic science studies have also suggested plausible biological mechanisms. The study from the Struhl lab suggests a potential new pathway through which metformin could have an effect on breast cancer cells, according to Ligibel.

In their search for compounds that selectively destroy cancer stem cells, researchers hope to improve cancer outcomes. But the story is never as simple in human cancers, according to Kornelia Polyak, M.D., Ph.D., a breast cancer researcher at the Dana-Farber Cancer Institute and an associate professor of medicine at Harvard Medical School.

Cancer stem cells are a shifty target, said Polyak, who was not involved in the current study. For example, any cancer cell can acquire the properties of a cancer stem cell, and cancer stem cells can change into non-stem cancer cells, which can be just as deadly. Clinical trials in people are needed to test these ideas, according to Polyak.

The study by Struhl and colleagues is an offshoot of a larger project in his lab to systematically track how gene activity changes when cells transform into cancer. These changes were remarkably similar to gene dynamics in diabetes and other inflammatory conditions.

The researchers reasoned that if a common genetic pathway underlies different diseases, drugs that work against one disease might work against another. In a screen, the most effective drug inhibiting the transformation of cells into cancer was metformin, which led to the experiments in this study. They were further encouraged by the low dose of metformin needed for the effect in the laboratory, compared to the amount needed for analogous molecular experiments in basic diabetes research. The relative dosage for treating or preventing cancer is unknown and untested in people.

Struhl and Harvard Medical School have applied for a patent for a combined therapy of metformin and a lower dose of chemotherapy, which is being tested in animals. The National Institutes of Health and the American Cancer Society funded this research.

Source: American Association for Cancer Research