* Each treatment cycle lasts 4 weeks (28 days). Participants will take metformin twice a day for all 28 days (except for the first 7 days of the first cycle when they will take it just once daily.)
* The following procedures will be done on Day 1 of treatment cycles 1, 2, 4, 7 and 10: medical history review, performance status, physical exam, blood tests.
* If the participant's first computed tomography (CT) or bone scan at the time of screening showed evidence of cancer, CT and bone scans will be repeated on Day 1 of treatment cycles 4, 7 and 10.
* Participants will be in this research study for about 12 months.
