The team found that estrogen and the chemicals caused the mammospheres to increase in numbers and size. However, with metformin added, the numbers and size of the mammospheres were dramatically reduced. While each of the chemicals enhanced growth by different means, metformin seemed to be able to inhibit their stimulated growth in all cases.

"While future studies are needed to understand the exact mechanism by which metformin works to reduce the growth of breast cancers, this study reveals the need to determine if the drug might be used as a preventive drug and for individuals who have no indication of any existing cancers," he said.

"Though we still do not know the exact molecular mechanism by which it works, metformin seems to dramatically affect how estrogen and endocrine-disrupting chemicals cause the pre-existing breast cancers to grow."

In addition, further research needs to be done with human cultures to see if metformin can reduce the risk of pancreatic and liver cancers in Type-2 diabetics as well, he said.

Source: Michigan State University