Metformin starting at a dose of 500 mg twice a day, orally with meals. After one week, increase the dose of metformin to 1000 mg as the first dose of the day and 500 mg as the second dose. After another week, increase to 1000 mg of metformin two times a day. Metformin treatment will be initiated one week before beginning chemotherapy, if possible, but chemotherapy will not be delayed for metformin loading.