Study Finds Metformin May Reduce Lung Cancer Risk Among Diabetic Nonsmokers
A large retrospective cohort study of diabetic patients taking metformin, a first-line treatment for type II diabetes, has found that while metformin use was not associated with lower lung cancer risk overall, the risk was 43% lower among diabetic patients who had never smoked. In addition, the risk appeared to decrease with longer use. Nonsmokers who used metformin for 5 years or longer had a 52% reduction in lung cancer risk. However, the finding was not statistically significant. The study by Sakoda is published in Cancer Prevention Research.
Study Methodology
The researchers analyzed data from patients in the KPNC Diabetes Registry who had completed a health survey administered from 1994 to 1996 and were 40 years old or older. Patients were defined as ever-users of a given diabetes medication if they had filled that prescription two or more times within a 6-month period. Information on their diabetes medications was collected from electronic pharmacy records.
In all, 47,351 diabetic patients (54% men) met the study eligibility criteria. Follow-up for incident lung cancer occurred from 1997 to 2012. Using Cox regression, the researchers estimated lung cancer risk associated with new use of metformin, along with total duration, recent use, and cumulative dose, adjusting for potential confounding factors.
Study Findings
During the 15 years of follow-up, 747 patients were diagnosed with lung cancer; of those patients, 80 were nonsmokers and 203 were current smokers. The researchers found that metformin use was not associated with lower lung cancer risk overall. However, the risk was 43% lower among diabetic patients who had never smoked, and the risk appeared to decrease with longer use. Nonsmokers who used metformin for 5 years or longer had a 52% reduction in lung cancer risk, but the finding was not statistically significant.
Using metformin for 5 years or more was associated with a 31% decrease in the risk for adenocarcinoma, the most common type of lung cancer found in nonsmokers and an 82% increase in the risk of small-cell carcinoma, a lung cancer commonly 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,” Lori C. Sakoda, PhD, MPH, a research scientist at the Kaiser Permanente Division of Research in Oakland, California, and corresponding author of the study, said in a statement. “However, our results suggest that risk might differ by smoking history, with metformin decreasing risk among nonsmokers and increasing risk among current smokers. 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.”
Dr. Sakoda is the corresponding author for the Cancer Prevention Research article.
The study was funded by the National Institutes of Health. Assiamira Ferrara, MD, PhD, reported receiving a commercial research grant from Takeda. Laurel A. Habel, PhD, reported receiving a commercial research grant from Takeda, Sanofi, and Genentech.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
