Effect of Metformin on Biomarkers of Colorectal Tumor Cell Growth

Inclusion Criteria: * Male or female, all races and ethnicities are eligible * Age equal to or greater than 18 years of age * All subjects should have a pathological/histological diagnosis of colorectal cancer. * Clinical diagnosis of stage I, II, III or IV colon cancer or stage I, II, III or IV rectal cancer; cancer may be primary including a secondary primary * Candidate for elective surgery(for removal of primary) or endoscopic biopsy * ECOG Performance status of 0 - 2 * Adequate renal, liver, and bone marrow function * Hb: (adequate for surgical intervention, with transfusion if necessary) * WBC: (normal range) * Platelets: (180K/cmm) * LFTs: Normal bilirubin (\< 2.0mg/dL), AST/ALT (2xULN) * Renal function: normal creatinine * Subjects must have signed informed consent * Female subjects must either not be of child-bearing potential or must have a negative urine pregnancy test within 7 days of beginning the drug or placebo treatment. Subjects are considered not of child-bearing potential if they are surgically sterile or they are postmenopausal for greater than 12 months. Exclusion Criteria: * Previously diagnosed with diabetes mellitus Type 1 or Type 2. * Currently taking biguanides, sulfonylurea drugs, thiazolidinediones, insulin, or mTOR inhibitors or having taken any of these medications during the 12 weeks prior to study participation. * Currently taking any non-steroidal anti-inflammatory drugs (NSAIDs) or aspirin and unable to stop such medications due to a present medical condition. * Clinical symptoms of gastrointestinal obstruction or bleeding and consideration for immediate surgery or immediate neoadjuvant chemoradiation. * Familial Adenomatous Polyposis (FAP), hereditary non-polyposis colorectal cancer (HNPCC), Putz-Jeghers disease, ulcerative colitis, or Crohn's disease. * Pregnant or lactating. * History of lactic or other metabolic acidosis. * Known hypersensitivity to Metformin. * Uncontrolled infectious disease. * History of Positivity for human immunodeficiency virus (HIV). * History of congestive heart failure requiring pharmacologic treatment. * History of excessive alcohol abuse, defined by a habitual intake of more than three drinks daily. * Previous or concurrent malignancies, except non-melanoma skin cancers, unless curatively treated and with no evidence of recurrence for \> 5 years, with the exception of prior CRC which has been treated and the patient has been in remission and the current primary tumor is a second CRC. * Unable to swallow and retain oral medication. * Mal-absorption syndrome, disease affecting gastrointestinal function, or previous resection of the stomach or small bowel. * Current use of medications for weight loss. * Currently taking cimetidine, thiazide diuretics or cephalexin. If a patient needs some of these agents, alternative agents should be substituted. * If the physician feels that the candidate is not suitable for the study, he/she will be excluded.