In the September issue of Cancer Prevention Research, two studies (a small clinical trial and an animal study) suggested that metformin might suppress the development of precancerous colorectal lesions in humans and prevent tobacco-induced lung cancers in mice.
In the first study, researchers from Yokohama City University School of Medicine in Japan randomized 12 nondiabetic patients with of rectal aberrant crypt foci (ACF- a marker of colorectal cancer) to treatment with metformin (250 mg/day) and 14 to no treatment. After 1 month, the metformin patients not only had fewer ACFs, they also had significant decreases in the proliferating cell nuclear antigen index.
In the second study, a research team from the National Cancer Institute (NCI) Medical Oncology, test cancer-preventive role of metformin in a mouse model. They exposed mice to the tobacco carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and then treated the mice with metformin in drinking water.
After about 12 weeks, mice that were treated with metformin had a 33% reduction in lung tumor multiplicity and a 34% reduction in tumor size, when compared with mice that did not get metformin.
Researchers postulated that metformin might change the cellular energy metabolism in a way that is particularly bad for cancers and precancerous cells. For example, it is believed that metformin is able to reduce levels of hormones that can stimulate cell growth, including insulin itself.
Source: Cancer Prev Res (Phila Pa). 2010;3:1049-1052, 1060-1065, 1066-1076, 1077-1083.
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