 The purpose of this pilot study is to use a pre surgical intervention model to evaluate the biologic effects of metformin in women with newly diagnosed early invasive breast cancer. Metformin is a biguanide derivative which is commonly used to treat patients with diabetes. This model will be used to evaluate the effects of metformin on a specific molecular pathway called the AMPKmTOR signaling pathway in the tumor. The effects of metformin on serum insulin levels and components of the insulin resistance syndrome will also be studied. 