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The use of metformin and the incidence of lung cancer in patients with type 2 diabetes

Smiechowski BB, Azoulay L, Yin H, Pollak MN, Suissa S

Diabetes care, 2013

1,061 participants

Abstract

OBJECTIVE: Observational studies have associated metformin use with a decreased risk of lung cancer incidence in patients with type 2 diabetes, but the studies had important methodological shortcomings. The objective of this study was to determine whether metformin use is associated with a decreased risk of lung cancer in patients with type 2 diabetes, while avoiding previous biases.

RESEARCH DESIGN AND METHODS: Using the U.K. General Practice Research Database, we assembled a cohort of patients newly treated with oral hypoglycemic agents (OHAs) between 1988 and 2009. A nested case-control analysis was conducted, where case subjects with lung cancer occurring during follow-up were matched with up to 10 control subjects for age, sex, calendar time, and duration of follow-up. Conditional logistic regression was used to estimate adjusted rate ratios of lung cancer associated with ever use of metformin, along with measures of duration and cumulative dose. Models were adjusted for potential confounders, which included smoking.

RESULTS: The cohort included 115,923 new users of OHAs, with 1,061 patients diagnosed with lung cancer during follow-up (rate 2.0/1,000 person-years). Metformin use was not associated with a decreased rate of lung cancer (rate ratio 0.94 [95% CI 0.76-1.17]). No dose-response was observed by number of prescriptions received, cumulative duration of use, and dose.

CONCLUSIONS: Metformin use is not associated with a decreased risk of lung cancer in patients…

How strong is the evidence?

Evidence Hub reads this as a case-control, done in people. Its evidence level is 4 of 5 (Low · observational). Observational designs can show an association but not prove cause. Reported size: 1,061 participants or records.

How the five levels of evidence work. The level is assigned automatically from the abstract and can be wrong, so check the paper.

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