ASCO Results: Diabetes Drug Shows Promise in Cancer Treatment, Prevention

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The first study sheds light on the complex interaction between underlying metabolic risk and breast cancer.

The most basic of diabetes drugs—metformin—improved survival for breast cancer patients and could prove effective in treating those with endometrial hyperplasia, according to results being presented at the American Society for Clinical Oncology in Chicago.

Researchers from the Perelman School of Medicine at the University of Pennsylvania presented 2 studies, the first of which looked at the effects of metformin on breast cancer survival rates. Authors found the relationship between use of the drug and survival was not straightforward and reflected “the complex interaction between underlying metabolic risks and breast cancer outcomes,” according to a statement.

Overall, results showed that patients who used metformin before being diagnosed with breast cancer were more than twice as likely to die than patients who never used the drug, while patients who began using metformin after diagnosis were nearly 50% more likely to survive.


Additional analysis showed that patients who used metformin were more likely to be over age 50 and be African-American. Those who used the drug before diagnosis were more likely to have ER/PR positive tumors, while those who used it afterward were more likely to have HER2+ and triple negative tumors. Thus, the authors report there is “compelling biological evidence” that differences in breast cancer tumor markers are related to differences in the way cancer develops in patients who are taking metformin.

“While the use of the drug may have a survival benefit for some breast cancer patients, those who developed breast cancer while already using metformin may have more aggressive cancer subtypes,” said Yun Rose Li, MD, PhD, the lead author and a fellow in the Endocrine and Oncology Surgery division at Perelman.

The second study looked at using metformin to treat endometrial hyperplasia, which occurs when there is hormonally unbalanced growth of the uterine lining that leaves patients at higher risk of cancer.

Eighteen patients in a trial took metformin for 3 months. Of the group, 56% responded to treatment, which was complete resolution of the hyperplasia. Women with simple hyperplasia responded especially well.

Metformin could be an alternative to the typical treatment of progesterone, which can cause weight gain, mood changes, and other side effects, according to Emily Ko, MD, MSCR, assistant professor in Obstetrics and Gynecology at Perelman. “Future studies may better identify women for which metformin may be most beneficial, as well as the most effective dosing regimens,” she said.