Diabetes drug may lower cancer risk in diabetic nonsmokers

Diabetic nonsmokers who take the diabetes drug metformin have a significantly lower risk of developing lung cancer, a new study has claimed. 

Among nonsmokers who had diabetes, those who took the diabetes drug metformin had a decrease in lung cancer risk, according to the study by Lori Sakoda, research scientist at the Kaiser Permanente Division of Research in US. 

Some laboratory studies and a number of observational studies suggest that metformin may prevent cancer, but the data from human studies, however, are conflicting, said Sakoda. 

The researchers conducted the study to further clarify the association between metformin use and lung cancer risk. 

Sakoda and colleagues conducted a retrospective cohort study of 47,351 diabetic patients (54 per cent men), 40 years or older, who completed a health-related survey between 1994 and 1996. 

Information on their diabetes medications was collected from electronic pharmacy records. About 46 per cent of them were "ever-users" of metformin, defined as those who filled two or more prescriptions within a six-month period. 

During 15 years of follow-up, 747 patients were diagnosed with lung cancer. Of them, 80 were nonsmokers, and 203 were current smokers. 

Metformin use was not associated with lower lung cancer risk overall; however, the risk was 43 per cent lower among diabetic patients who had never smoked, and the risk appeared to decrease with longer use. 

Nonsmokers who used metformin for five years or longer had a 52 per cent reduction in lung cancer risk, but this finding was not statistically significant. 

Metformin use for five or more years was associated with a 31 per cent decrease in the risk for adenocarcinoma, the most common type of lung cancer diagnosed in nonsmokers, and an 82 per cent increase in the risk for small-cell carcinoma, a type of lung cancer often diagnosed in smokers, but neither of these findings were statistically significant. 

"Metformin use was not associated with lung cancer risk when we looked at all patients with diabetes. However, our results suggest that risk might differ by smoking history, with metformin decreasing risk among nonsmokers and increasing risk among current smokers," said Sakoda. 

The research was published in the journal Cancer Prevention Research.