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Lung Cancer Risk Reduction Seen in Nonsmokers on Metformin

But smokers taking the drug may have slightly increased risk….

Diabetic nonsmokers who had taken metformin had a decreased risk of lung cancer compared with metformin non-users, researchers said.

A retrospective analysis covering 47,351 diabetic patients 40 and older found that, while metformin use was not associated with lower lung cancer risk overall, versus non-users, the risk was 43% lower among those who had never smoked, Lori Sakoda, PhD, of Kaiser Permanente Division of Research in Oakland, and colleagues reported.

“Our results suggest that risk might differ by smoking history, with metformin decreasing risk among nonsmokers and increasing risk among current smokers,” said Sakoda in a press release.

The findings “were unexpected,” she added. “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.”

During 15 years of follow-up, 747 patients were diagnosed with lung cancer. Of them, 80 were nonsmokers, and 203 were current smokers. Cox regression was used to estimate lung cancer risk associated with new use of metformin.

The study found no association between duration, dose, or recency of metformin use with overall lung cancer risk. However, compared with never-use, ever-use of metformin among never-smokers was inversely associated with lung cancer risk with further decrease with metformin use of at least 5 years, although not statistically significant.

Consistent with this variation in effect by smoking history, longer use showed a trend toward lower risk of adenocarcinoma, the most common type of lung cancer diagnosed in nonsmokers, but risk of small cell carcinoma, a type of lung cancer often diagnosed in smokers, trended higher. Neither of these findings were statistically significant.

Practice Pearls:

  • Diabetic nonsmokers who had taken metformin had a decreased risk of lung cancer.
  • The study found no association between duration, dose, or recency of metformin use with overall lung cancer risk.
  • In obese, hyperinsulinemic mice, the drug appears to suppress lung tumor growth by increasing insulin sensitivity and inhibiting mTOR.

Sakoda L, et al “Metformin use and lung cancer risk in patients with diabetes” Cancer Preven Res 2015; DOI: 10.1158/1940-6207.CAPR-14-0291.