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