The Use of Metformin and the Incidence of Lung Cancer in Patients With Type 2 Diabetes

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Title: Metformin use and lung cancer risk Running head: metformin and lung cancer

Shih-Wei Lai, MD1,2_{;Kuan-Fu Liao, MD and MS}3,4,5

1_{School of Medicine, China Medical University, Taichung, 404, Taiwan}

2_{Department of Family Medicine, China Medical University Hospital, Taichung, 404,} Taiwan

3_{Department of Internal Medicine, Taichung Tzu Chi General Hospital, Taichung,} 427, Taiwan

4_{School of Medicine, Tzu Chi University, Hualien, 970, Taiwan}

5_{Department of Health Care Administration, Central Taiwan University of Science} and Technology, Taichung, 406, Taiwan

Corresponding author: Kuan-Fu Liao, MD and MS

Department of Internal Medicine, Taichung Tzu Chi General Hospital, No.66, Sec. 1, Fongsing Rd., Tanzi District, Taichung City, 427, Taiwan

Phone: 886-4-2205-2121 Fax: 886-4-2203-3986

E-mail: [email protected]

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To editor,

One cohort study recently published in Diabetes Care with interest about the

association between metformin use and lung cancer risk, Smiechowski and colleagues have reported that metformin use can not correlate with decreased risk of lung cancer in patients with type 2 diabetes (rate ratio = 0.94, 95% CI = 0.76–1.17) . However, one well-designed meta-analysis by Noto and colleagues has shown that metformin use can correlate with decreased risk of lung cancer in diabetic patients (risk ratio = 0.67, 95% CI =0.45-0.99) . Noto and colleagues have carefully selected the best studies and no methodological shortcomings of these cited studies can be found. Moreover, in our cohort study, metformin use might correlate with decreased risk of lung cancer in diabetic patients (hazard ratio = 0.55, 95% CI = 0.37-0.82) . We have discussed that though the real mechanism of the observed risk reduction of lung cancer is not clear, it is more plausible that unmeasured factors associated with the metformin use may partially explain the association of decreased risk .

To our opinion, the exact role of metformin use on lung cancer risk cannot be completely determined from existing data. Hence, more prospective clinical trials of metformin in non-diabetic individuals are needed to explicitly clarify this major public health problem.

Conflict of Interest Statement: The authors disclose no conflicts of interest.

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REFERENCES

1. Smiechowski BB, Azoulay L, Yin H, Pollak MN, Suissa S: The Use of metformin and the incidence of lung cancer in patients with type 2 diabetes. Diabetes Care 2012; (online paper)

2. Noto H, Goto A, Tsujimoto T, Noda M: Cancer risk in diabetic patients treated with metformin: a systematic review and meta-analysis. PLoS One 2012;7:e33411 3. Lai SW, Liao KF, Chen PC, Tsai PY, Hsieh DP, Chen CC: Antidiabetes drugs correlate with decreased risk of lung cancer: a population-based observation in Taiwan. Clin Lung Cancer 2012;13:143-148