Metformin, a widely used, well-tolerated drug prescribed for patients with diabetes, may protect against liver cancer, according to a study published in Cancer Prevention Research, a journal of the American Association for Cancer Research.

The study, led by Geoffrey Girnun, Ph.D., an assistant professor in the department of biochemistry and molecular biology at the University of Maryland School of Medicine, is one more in an ongoing look at the effect of metformin in cancer prevention. However, it is one of the first to evaluate liver cancer.

"Since many of the effects of the drug take place in the liver, we were surprised when we reviewed the literature that there was no direct evidence for a protective effect of metformin in liver cancer except for a few retrospective epidemiological studies," said Girnun.

He and his colleagues chemically induced liver tumors in mice. The mice taking metformin displayed minimal tumor activity, while the control mice displayed significant tumor growth.

Girnun's team also showed that metformin prevented liver cancer in part by inhibiting lipid synthesis in the liver, a process known to promote cancer. Patients with diabetes, obese individuals, patients with hepatitis or patients with nonalcoholic fatty liver disease are at the greatest risk for liver cancer. All these diseases are associated with increased lipid synthesis. While diabetic patients are already prescribed metformin for their conditions, according to Girnun, the mechanism by which metformin prevents liver cancer may be transferable to these other patient populations at risk for liver cancer.

"So we are talking about a targeted population that will receive this benefit," he said.

Girnun is currently planning a clinical trial in patients at risk for liver cancer to determine if the chemopreventive qualities observed in mice are confirmed in humans.