Metformin treatment has been shown in research to provide a significant decrease in risk of cancerous cell growth and thus a decrease in risk of cancer overall. A recent meta-analysis has confirmed that patients with Type 2 diabetes who undergo metformin treatment are similarly at a significantly reduced risk of developing colorectal cancer — a 37 percent decrease in risk. The results were published in the October 2011 issue of the journal “Diabetes Care,” the journal of the American Diabetes Association.

“The results indicate that metformin therapy was associated with an estimated reduction of 37% in the risk of colorectal cancer among patients with type 2 diabetes,” said the researchers on the project.

The meta-analysis was conducted at Shanghai Jiao Tong University in China and was headed by Zhi-Jian Zhang, M.D., Ph.D., with the department of epidemiology and biostatistics at the School of Public Health division of the university. Dr. Zhang’s research team pooled together the existing data from studies that investigated the effects of metformin treatment on colorectal cancer in patients with Type 2 diabetes. Information was pulled from the SciVerse Scopus and PubMed databases, comprising five studies that had been published between January 1966 and March 2011. In all, data from 108,161 patients was identified and used to analyze trends in metformin treatment as it related to risk of colorectal cancer in Type 2 diabetics.

The researchers found that metformin therapy was associated with significantly decreased risk of colorectal neoplasm when compared to patients who received non-metformin treatment (RR=0.63; 95% CI, 0.50-0.79).

The research team did not include one of the identified studies, which had been conducted on colorectal adenoma. After the exclusion of that study, the data of 107,961 diabetes patients remained, with 589 cases of colorectal cancer occurring during the follow-up periods of the four remaining studies. After the findings were adjusted to exclude the study on colorectal adenoma, researchers still found that metformin therapy was associated with significantly reduced risk of developing colorectal cancer (RR=0.63; 95% CI, 0.47-0.84).

The researchers stated that they did not find any evidence which would suggest significant heterogeneity across the studies (P=.30).

According to the research team, metformin may help fight the growth of cancer cells due to its role in the tumor suppressor pathway, where it activates AMP-activated protein kinase (9) and is also a part of the sequence that activates LKB1, a gene that is known to suppress tumors. Additionally, in vitro studies have shown that metformin actually selectively kills cancer stem cells. Those findings have been confirmed in rodent experiments, which also showed that metformin inhibited carcinoma growth in the colon.

The authors noted that previous research has tested the effects of metformin on non-diabetic humans with rectal aberrant crypt foci — one of the earliest warning signs that the individual may develop colon cancer. The findings of that study demonstrated that one month of metformin treatment was associated with a decrease in aberrant crypt foci compared to a control group who did not receive metformin treatment.

The researchers commented that if metformin therapy is definitively proven in further research to significantly reduce risk of colorectal cancer, it will likely be prescribed to most diabetics as a measure to manage blood glucose levels and also to prevent cancer.

“If metformin therapy ultimately proves effective on reducing the risk of colorectal cancer, it would likely be recommended for the overwhelming majority of diabetes patients for both blood glucose control and cancer prevention,” said the researchers.