Impact of Pretreatment With Metformin on Colorectal Cancer Stem Cells (CCSC) and Related Pharmacodynamic Markers

Inclusion Criteria: * Histologically documented colorectal cancer * Intent to undergo disease resection or biopsy at least 7days from the treatment start date (allowing for a minimum of 5 days of treatment plus 2 days break) * Medically fit for resection of their primary tumor or for biopsy * Age 18-79 years * Adequate renal function (serum creatinine levels \<1.5 mg/dL \[males\], \<1.4 mg/dL \[females\] or estimated creatinine clearance \>= 60 ml/min) * Adequate hepatic parameters, including aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels ≤ 2.5 x upper limit of normal (ULN), total bilirubin ≤ 1.5 x ULN, and alkaline phosphatase levels ≤ 2.5 x ULN * Ability to understand and willingness to sign a written informed consent document Exclusion Criteria: * Intent to administer neoadjuvant chemotherapy or radiation therapy prior to the surgery or biopsy; * Intent to perform surgery or biopsy within 7 days of study treatment start; * Any situation where participation in this trial would alter, or cause significant risk of altering the ability or timing of a subject to undergo resection of their tumor * Current use of metformin (within the past month); * Blood glucose using point of care test \< 70mg/dl; * Renal disease or renal dysfunction not meeting inclusion criteria; * Significant medical conditions such as cardiovascular collapse (shock), acute myocardial infarction, septicemia, acute or chronic metabolic acidosis * History of, or states associated with, lactic acidosis such as shock or pulmonary insufficiency, alcoholism (acute or chronic), conditions associated with hypoxemia and pancreatitis * Severe dehydration * Clinical or laboratory evidence of hepatic disease * Congestive heart failure requiring pharmacologic treatment, or unstable or acute congestive heart failure * Known hypersensitivity to metformin hydrochloride * Pregnant or lactating women * Psychiatric illness or social situation that would limit compliance with study requirements and/or obscure results