The effect of metformin on proliferation, apoptosis and downstream signaling pathways will be compared between pre-treatment endometrial biopsies and post-treatment hysterectomy specimens. Tissue microarrays will be constructed and immunohistochemstry performed to evaluate proliferation, apoptosis and changes in critical signaling pathways mediated by metformin, and these findings will be correlated with our in vitro preclinical studies. Fresh tissue will also be obtained, and Western immunoblotting will be used to assess expression of the phosphorylated forms of the downstream targets of metformin. The hypothesis is that treatment with metformin will result in a decrease in proliferative markers and an increase in markers of apoptosis in the endometrial cancer tumors. AMPK phosphorylation and inhibition of critical downstream targets of the mTOR pathway will be seen in the post-treatment hysterectomy specimens. Metabolomic profiling will also be performed of tumors and associated biofluids (i.e. serum and urine) before and after treatment with metformin to identify potential biomarkers of response to this therapy.