In mice, pretreatment with the diabetes drug prevented the otherwise dramatic ability of human breast cancer stem cells to form tumors. In other mice where tumors were allowed to take hold for 10 days, the dual therapy also reduced tumor mass more quickly and prevented relapse for longer than doxorubicin alone. In the two months between the end of treatment and the end of the experiment, tumors regrew in mice treated with chemotherapy alone, but not in mice that had received both drugs. By itself, metformin was ineffective in treating tumors.
"This is an exciting study," said Jennifer Ligibel, a medical oncologist at Dana-Farber Cancer Institute and an HMS instructor in medicine, who was not involved in the study. Ligibel and colleagues at the National Cancer Institute of Canada Clinical Trials Group are developing a large-scale phase II trial to study metformin's impact on recurrence in women treated for early stage breast cancer.
"There is a lot of interest in studying metformin in breast cancer, but so far we do not have direct evidence that metformin will improve outcomes in patients," Ligibel said. "That's what this trial is for."
So far, observational studies have suggested a lower risk of cancers, including breast cancer, and better response to chemotherapy in diabetics taking metformin, she said. Basic science studies also have 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, she said.
In their search for compounds that selectively destroy cancer stem cells, scientists hope to improve cancer outcomes. But the story is never as simple in human cancers, said Kornelia Polyak, a breast cancer researcher at
|Contact: Carol Cruzan Morton|
Harvard Medical School