Research in context
Evidence before this study
We searched PubMed between Jan 1, 1990, and Sept 1, 2011, using the terms “colorectal cancer”, “chemoprevention”, “metformin”, and “clinical trial”. We searched for articles published in English only. We found no clinical trial data related to the use of metformin for colorectal cancer chemoprevention. As a preliminary study before considering long-term colorectal cancer chemoprevention trials, we devised a 1-year clinical trial to assess the safety and the chemopreventive effect of metformin against the development of metachronous colorectal adenomas or polyps in patients without diabetes post-polypectomy.
Added value of this study
To our knowledge, this is the first comparative randomised trial to assess the chemopreventive effect of metformin for metachronous colorectal adenomas and polyps. Low-dose metformin reduced the incidence and number of metachronous adenomas and polyps after polypectomy. The 1-year administration of low-dose metformin was safe for non-diabetic patients.
Implication of all the available evidence
Recent evidence indicates that metformin has a suppressive effect on tumorigenesis and cancer cell growth by activating AMPK and suppressing the mTOR pathway. Many metformin chemoprevention trials against various types of cancer are in progress. Our findings suggest that metformin has a potential role in the chemoprevention of colorectal cancer.