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Metformin is used widely in the treatment of type 2 diabetes. It has off-label indications for use in the prevention of diabetes and in hyperinsulinar obesity. In medical practices, the implementation of metformin for these off-label indications is variable, often at the level of the provider. Multiple retrospective investigations have also shown a clinical benefit in men with prostate cancer who are incidentally treated with metformin. This pragmatic study will test the feasibility of enrolling patients who have glucose intolerance (as defined by HbA1c of 5.7-6.4%) and/or who have increased BMI (BMI greater than or equal to 25 kg/m2) to a randomized pragmatic study of metformin plus lifestyle modification information versus lifestyle modification information only. For purposes of the scope of this project and the study's feasibility, this will be implemented in a group of prostate cancer patients, who may have additional benefits from metformin.

In this study, subjects with prostate cancer will be randomized to metformin plus educational material for lifestyle modification versus educational material for lifestyle modification alone and followed for up to 10 years. Population-based, retrospective studies have reported improved outcomes, including prostate cancer specific mortality, with the incidental use of metformin in prostate cancer patients. One prominent study is this area from Margel, et al was published in 2013.2 Using the administrative database from several Ontario health districts, men aged 66 with incidental diabetes and prostate cancer antigen (PCA) were studied. The study included over 3000 men and found an adjusted hazard ratio of 0.76 (95% CI, 0.64 to 0.89) for PCA-specific mortality for each additional 6 months of metformin use. There was no relationship to survival with any other diabetic medication. In addition to the use of metformin for the prevention of metabolic complications related to obesity and the prevention of diabetes, there are several studies reporting a potential benefit in those with prostate cancer. In a Veterans Administration-based study, more than 87,000 subjects were identified with PCA in the sample.3 The subjects were analyzed in 3 cohorts: 1) no diabetic medication (DM), 2) DM without metformin use and 3) DM with metformin use. Men with DM who were treated with metformin were found to have improved OS (HR 0.82, 95% CI 0.78 - 0.86, for mortality) compared to men with DM not on metformin. Reduced cancer specific mortality was also observed in the men with DM on metformin (HR 0.70, 95% CI 0.64 -0.77) in comparison to men with DM not taking metformin (HR 0.93, 95% CI 0.85 -1.00) - the reference group were those without DM. Despite considerable interest in these findings, there is little if any prospective data on the use of metformin in this setting.