Evaluation of the Molecular Effects of Metformin on the Endometrium in Patients With Endometrial Cancer

The Study Drug: Metformin is designed to treat both diabetes and insulin resistance. Both diabetes and insulin resistance have been linked to endometrial cancer. Although you do not have a diagnosis of diabetes, metformin may still have an affect on your cancer cells. Study Visit (before taking Metformin): If you are found eligible to take part in this study, you will have a study visit before you begin taking Metformin. The following tests and procedures will be performed: * Blood (about 2 tablespoons) and urine will be collected for research to look at different hormone levels. * If needed, a fasting glucose level will be obtained. * If you are found not to be eligible your blood, urine, and tissue for research will be discarded. Study Drug Administration: You will take metformin, by mouth, 1 time each morning, with breakfast, for at least 7 days and up to 30 days until your scheduled surgery is performed. You will record the dates and times you take metformin on a study drug calendar provided by the study staff. You will not take metformin on the day of your surgery. Study Tests (on the day of your surgery): You will bring your study drug calendar to the clinic on the day of your surgery. The following tests and procedures will also be performed: * Blood (about 2 tablespoons) and urine will be collected for routine tests and to check different hormone levels. * During surgery, you will have a second endometrial biopsy for biomarker testing. Length of Study: You will be off study after your surgical procedure. This is an investigational study. Up to 30 women will take part in this study. Up to 25 participants will take part at MD Anderson.