Exercise and Metformin in Colorectal and Breast Cancer Survivors

Metformin is a medication that is commonly used in the treatment of diabetes. Recently small studies in cancer patients without diabetes suggest that metformin may benefit in lowering insulin levels. In those studies of patients with cancer but not diabetes, glucose (or sugar) levels in the blood are generally no lowered. Insulin and insulin-like growth factors affect the growth of cancer cells. This randomized study will compare different interventions; exercise, exercise and metformin, metformin alone, or a control arm. The investigators are not directly testing how either exercise or metformin affects your disease. The investigators are testing how they affect insulin levels in your body as well as other blood markers. The investigators believe that these blood tests may either be related to cancer recurrences or be an early sign of cancer recurrences and they are testing how both exercise and metformin may change those markers.

Subjects will be randomized into one of four groups: exercise training, exercise training and metformin, metformin alone, or control arm. All subjects will have lifestyle measurements, interviews regarding activity level, diet questionnaires, and blood tests. Subjects randomized to exercise training will participate in two supervised exercise sessions per week with an exercise physiologist for 3 months. They will also be asked to exercise on their own for up to an additional 120 minutes each week. Subjects randomized to exercise training and metformin will participate in two supervised exercise sessions per week and will take metformin. Metformin will be taken once daily for the first two weeks and then twice daily for 3 months. Subjects randomized to metformin will take metformin once daily for the first two weeks and then twice daily. Subjects on the control arm will receive a packet of educational information on nutrition and physical activity developed by the National Cancer Institute and American Cancer Society. In addition to education information, they will be offered two supervised sessions with an exercise physiologist as well as a pedometer 3 months after enrollment in the study.