Nonsmokers with diabetes treated with metformin appeared to have a lower risk for lung cancer, new data published in Cancer Prevention Research indicate.
Results from studies evaluating the link between metformin and lung cancer have been mixed, according to background information in the article.
To further examine this relationship, Lori Sakoda, PhD, MPH, of the Kaiser Permanente Division of Research in Oakland, California, and colleagues conducted a retrospective cohort study of 47,351 patients with diabetes aged at least 40 years (54% men) who completed a health-related survey between 1994 and 1996.
The researchers gleaned information on diabetes medications using electronic pharmacy records. Of all patients included in the study, about 46% were ever users of metformin, which was defined as filling two or more prescriptions with a 6-month period.
Follow-up for incident lung cancer lasted from Jan. 1, 1997 to June 30, 2012.
A total of 747 patients were diagnosed with lung cancer during 428,557 person-years of follow-up — 80 of whom were nonsmokers and 203 who were current smokers, according to the data.
Results indicated no link between metformin use and lung cancer risk overall, though the researchers noted an inverse association between ever use of metformin and lung cancer risk in never smokers (HR=0.57; 95% CI, 0.33-0.99). This risk also appeared to decrease with longer use of the drug, with data demonstrating an HR of 0.48 (95% CI, 0.21-1.09) among those who had been taking metformin for 5 years or more.
Longer use of metformin was also associated with a decreased risk for adenocarcinoma (HR=0.69; 95% CI, 0.40-1.17) but an increased risk for small cell carcinoma (HR=1.82; 95% CI, 0.85-3.91).
“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,” Dr. Sakoda said in a press release.
“Our results suggesting that the risk associated with metformin might differ by smoking history were unexpected. Additional large, well-conducted studies are needed to clarify whether metformin may be used to prevent lung or other cancers, particularly in specific subpopulations, such as nonsmokers.”