Diabetic non-smokers taking metformin have lower lung cancer risk

Diabetic non-smokers taking metformin have a lower lung cancer risk compared with those who do not take metformin, according to a study published in Cancer Prevention Research.

LORI SAKODA, PhDLori Sakoda, PhD, Kaiser Permanente Division of Research in Oakland, and colleagues, conducted a retrospective cohort study of 47,351 Kaiser Permanente Northern California (KPNC) patients aged 40 years and older with diabetes who completed a health-related survey between 1994 and 1996, to examine the association between metformin use and lung cancer risk. Data on prescribed diabetes medications were ascertained from electronic pharmacy records, and cancers were identified from the KPNC Cancer Registry. Modern statistical methods were used to minimize potential biases that could impact study results.

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Follow up for incident lung cancer occurred from January 1, 1997, until June 30, 2012. Using Cox regression, researchers estimated lung cancer risk associated with new use of metformin, along with total duration, recency, and cumulative dose (all modeled as time-dependent covariates), adjusting for potential confounding factors. During 428,557 person-years of follow-up, 747 patients were diagnosed with lung cancer.

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No association was found with duration, dose, or recency of metformin use. Among those patients who never smoked, however, ever use was inversely associated with lung cancer risk and risk decreased monotonically with longer use. Among current smokers, corresponding risk estimates were >1.0, although not statistically significant, according to the study. Consistent with this variation in effect by smoking history, longer use was associated with lower adenocarcinoma risk, but higher small-cell carcinoma risk.

“When we looked at all patients with diabetes, metformin use was not associated with lung cancer risk,” Sakoda said. “However, we observed that risk might differ according to smoking history, with metformin decreasing risk among never smokers and increasing risk among current smokers. Based on our findings alone, it’s still too early to change clinical practice. However, if our findings can be confirmed, metformin might be beneficial to patients with diabetes who have never smoked.”

The finding that lung cancer risk associated with metformin could depend on smoking history is intriguing, but must be confirmed, according to the researchers.

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“It is also important that large, well-conducted studies are conducted to clarify whether metformin may be used to prevent lung or other cancers, particularly in subpopulations, such as never smokers,” Sakoda said.