The study, led by Geoffrey Girnun, assistant professor of biochemistry and molecular biology at the University of Maryland School of Medicine, looks at the effect of metformin in cancer prevention and 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," Girnun was quoted as saying in the journal Cancer Prevention Research.

He and his colleagues chemically induced liver tumours in mice. These mice taking metformin displayed minimal tumour activity, while the control mice (not given metformin) displayed significant tumour growth, said a university statement.

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.

Diabetics, obese individuals, patients with hepatitis or patients with non-alcoholic fatty liver disease are at the greatest risk for liver cancer.