metformin for breast cancer

I don't know the actual mechanism, and I am sure someone else who does will come along, but I believe metformin interferes with the tumors ability to get sugar.  There are many women out there now participating in a trial for metformin.  Initially, doctors noticed that women who had similar tumor characteristics, when one was on metformin the tumor tended to be smaller, less developed.  The hope is that women can take the metformin (with few side effects) and reduce the reoccurance of the breast cancer.