An Endometrial Cancer Chemoprevention Study of Metformin

Study Groups: If you are found to be eligible to take part in this study, you will be randomly assigned (as in the roll of dice) to 1 of 4 study groups: * Metformin only. * Placebo and lifestyle intervention. * Metformin and lifestyle intervention. * Placebo only. Neither you nor the study staff will know if you are receiving metformin or placebo. However, if needed for your safety, the study staff will be able to find out what you are receiving. In the first month you will gradually increase the dose of metformin/placebo by mouth as listed below: * Week 1: One capsule each day * Week 2: One capsule 2 times each day * Week 3: One capsule 3 times each day * Week 4: Two capsules 2 times each day After week 4, you will continue to take 2 capsules of metformin/placebo 2 times each day. If you are receiving the lifestyle intervention, you will have 16 lifestyle intervention sessions over 4 months. At each of these sessions, you will discuss methods for managing your weight. You will receive print materials and worksheets, measuring utensils, and a food scale. You will be instructed how to use each of these materials and how often to use them during the study. You will also be provided with opportunities for supervised exercise (such as group exercise class and group walks). If you are traveling during a scheduled session, it can be performed over the telephone. Each call should last about 30 minutes, during which you will discuss the same goals and information that you would discuss in the in-person sessions. Study Visits: Before you can begin receiving the study drug/placebo: * At the second screening visit , you will have a dual energy x-ray absorptiometry (DEXA) scan to measure your body composition. The scan requires you to lie still on a table for about 8-10 minutes while a low-energy x-ray takes an image that allows the study staff to get an image of your body fat density. * You will be given an accelerometer (a small, portable device that measures your physical activity) and be taught how to use it at the first Screening Visit. You will wear the accelerometer at all times while you are awake for 7 days. At the second Screening Visit, you will return the accelerometer at an intervention session. If you are not able to return it at the second visit then you will mail it back to the study staff in a pre-paid envelope. You will receive the accelerometer again at Month 4 and wear it for another 7 days. * You will receive a study diary in which you will record any and all exercise you perform each day while you are on study. It should take about 5 minutes to complete each time. * You will complete questionnaires about diet and exercise. These questionnaires should take about 30-40 minutes to complete. * You will also be taught to complete a questionnaire on the internet to record the food you eat in a 24 hour period. You will do this 3 times over a 2 week period. The first time, you will complete it at the clinic. The study staff will call and remind you to complete the questionnaire the other 2 times. Each time you complete this questionnaire, it should take about 40 minutes. At Month 1, all participants will return for a study visit. The following tests and procedures will be performed: * Blood (about 2 teaspoons) will be drawn for routine tests. If this blood draw shows that your liver or kidney function is abnormal, you will need to return for an additional blood °draw at Month 2. * If you are having symptoms that you would describe as moderate or worse, you will have a non-pelvic physical exam including measurement of your vital signs and any unreported symptoms you may be having. At each month, you will be asked about any symptom(s) that you may have to learn if it is related to the study. If you are called, this phone call should last about 5 minutes. If you are asked in a in-person visit, the visit can last up to an hour. Length of Study: You will receive the study drug/placebo and/or lifestyle intervention for up to 4 months. You will be taken off study if you have intolerable side effects or if you develop endometrial cancer or hyperplasia during the study. Your participation in the study will be over after the end-of-study visit. Post-Treatment Visit: At the end of the 4th month, you will have a post-treatment visit. You will repeat all procedures performed in the first and second visit: * Your height, weight, waist, and hip circumference will be measured. * You will have a DEXA scan. * You will complete the questionnaires about food, diet, and exercise. * You will be given a questionnaire about your satisfaction (based on the intervention) to complete and return at this visit. This questionnaire will take up to an hour to complete. * You will have an endometrial biopsy. * Blood (about 8 tablespoons) will be drawn for routine tests and for biomarker testing. You will have to fast (not eat or drink anything except water) for 12 hours before this blood draw. * You will complete the questionnaire on the internet to record the food you eat in a 24 hour period. You will do this 3 times over a 2 week period. The first time, you will complete it at the clinic. The study staff will call and remind you to complete the questionnaire the other 2 times. Each time you complete this questionnaire, it should take about 40 minutes. Follow-Up: About 1 year after the screening visits (+/- 1 month), the following tests and procedures will be performed: * Your height, weight, waist, and hip circumference will be measured. * You will have a DEXA scan. * Blood (about 8 tablespoons) will be drawn for routine tests and for biomarker testing. °You will have to fast (not eat or drink anything except water) for 12 hours before this blood draw. * You will wear the accelerometer for 7 days. * You will complete questionnaires about food, diet, and exercise. * You will complete the questionnaire on the internet to record the food you eat in a 24 hour period. You will do this 3 times over a 2 week period. The first time, you will complete it at the clinic. The study staff will call and remind you to complete the questionnaire the other 2 times. Each time you complete this questionnaire, it should take about 40 minutes. This is an investigational study. Metformin is FDA approved and commercially available for the treatment of diabetes and insulin resistance. Up to 100 patients will take part in this study. All will be enrolled at MD Anderson Cancer Center.