August 21, 2013
More Evidence That Metformin Helps Prevent Prostate Cancer Deaths in Diabetic Men

Toronto, ON—A recent Canadian study provides more evidence that metformin can play a role in preventing prostate cancer deaths in men with diabetes.

“Increased cumulative duration of metformin exposure after PC diagnosis was associated with decreases in both all-cause and PC-specific mortality among diabetic men,” according to the report published recently in the Journal of Clinical Oncology.

Based on previous research suggesting a positive effect, researchers evaluated the association between cumulative duration of metformin use after prostate cancer (PC) diagnosis and all-cause and PC-specific mortality among patients with diabetes.

Using a population-based retrospective cohort design, data were gathered from several Ontario health care administrative databases. Then, the effect of duration of antidiabetic medication exposure after PC on all-cause and disease-specific mortality was examined in a cohort of 3,837 men with diabetes—all older than age 66 years—who subsequently developed PC.

Median age at PC diagnosis was 75, and, during a follow-up of 4.64 years on average, 1,343 (35%) died—with 291 patients (7.6%) dying as a result of prostate cancer.

Cumulative duration of metformin treatment after PC diagnosis was associated with a significantly decreased risk of PC-specific and all-cause mortality in a dose-dependent fashion, the authors report, with adjusted HR for PC-specific mortality 0.76 (95% CI, 0.64-0.89) for each additional 6 months of metformin use. While the association with all-cause mortality was also significant, it declined over time from an HR of 0.76 in the first 6 months to 0.93 between 24 and 30 months, according to the report.

The study found no relationship between cumulative use of other antidiabetic drugs and prostate cancer outcomes.

An accompanying editorial from Kathryn L. Penney, ScD, and Meir J. Stampfer, MD, DrPH, of Brigham and Women's Hospital and Harvard School of Public Health in Boston, said the findings were significant and called for additional research.

“We agree with Margel et al that their findings clearly are insufficient to warrant recommendations to institute metformin treatment in men with prostate cancer,” Penney and Stampfer write. “However, their results provide a compelling rationale for conducting a large-scale long-term randomized trial of metformin in men with clinically localized disease to reduce prostate cancer-specific mortality as an urgent research priority.”

Metformin’s benefits may not be limited to prostate cancer, however. A meta-analysis published last year suggested, “A growing body of evidence has suggested that metformin potentially reduces the risk of cancer. Our objective was to enhance the precision of estimates of the effect of metformin on the risk of any-site and site-specific cancers in patients with diabetes.”

The study, which appeared in the online journal PLOS One, concluded that “the use of metformin in diabetic patients was associated with significantly lower risks of cancer mortality and incidence.” The authors point out, however, that their analysis was primarily based on observational studies and that long-term randomized trials also would be necessary to confirm the potential benefit.

U.S. Pharmacist Social Connect