Depending on their smoking history, a drug may have contrary effects on people suffering from diabetes – reducing lung cancer risk among nonsmokers and increasing the risk among smokers.
Among nonsmokers who had diabetes, those who took the diabetes drug metformin had a decrease in lung cancer risk, the findings showed.
"Our results suggest that risk might differ by smoking history, with metformin decreasing risk among nonsmokers and increasing risk among current smokers," said Lori Sakoda, research scientist at Kaiser Permanente Division of Research in Oakland, California.
The study involved 47,351 diabetic patients (54 percent men), 40 years or older, who completed a health-related survey between 1994 and 1996.
During 15 years of follow-up, 747 patients were diagnosed with lung cancer.
Metformin use was not associated with lower lung cancer risk overall; however, the risk was 43 percent lower among diabetic patients who had never smoked, and the risk appeared to decrease with longer use.
Metformin use for five or more years was associated with a 31 percent decrease in the risk for adenocarcinoma, the most common type of lung cancer diagnosed in nonsmokers, and an 82 percent increase in the risk for small-cell carcinoma, a type of lung cancer often diagnosed in smokers.
The study appeared in the journal Cancer Prevention Research.