The longer patients were treated with metformin after being diagnosed with prostate cancer, the greater their survival rates were, depending on the dose they were given….
In the retrospective cohort designed study, patient medical data was retrieved from different healthcare administrative databases from Ontario. A total of 3,837 male patients with diabetes were included in the study. Participants had to be aged 66 years or older, treated with anti-diabetic medication (specifically metformin), and had to have later developed prostate cancer.
The authors of the study analyzed the association between the duration patients were exposed to the metformin and all-cause and prostate cancer (PC) specific mortality. In order to interpret the effects of metformin on mortality, the authors calculated hazard ratios (HR) by using a time-varying Cox proportional hazard model.
The median age patients were diagnosed with prostate cancer was 75. After about a 5-year follow up of these patients, it was found that 1,343 died, and 291 died as a result of their prostate cancer. The results showed that the longer patients were treated with metformin after they had been diagnosed with prostate cancer, the greater their survival rates were, depending on the dose they were given as well. According to Margel et al, "Adjusted HR for PC-specific mortality was 0.76 (95% CI, 0.64 to 0.89) for each additional 6 months of metformin use." Duration of metformin use and all-cause mortality also had a significant association, but decreased over time since the HR went from 0.76 for the first 6 months to 0.93 between 24-30 months. No association was found among use of other anti-diabetic medications and mortality rates.
In conclusion, increased exposure to metformin among patients with diabetes and who were subsequently diagnosed with prostate cancer was associated with decreased mortality as a result of prostate cancer and other causes. The authors concluded "metformin may further improve survival as an adjunct therapy, even among those already receiving optimal cancer treatments." However, the authors of the study note that more randomized controlled trials are needed to test the validity of this association.
Limitations of the study included its observational design and lack of patient data since the databases did not include information such as severity of diabetes, BMI, lab values, and stage of prostate cancer.