Effect of Diabetes Mellitus and Metformin Usage on Treatment Outcomes and Side Effects on Prostate Cancer Treated with Radical Radiotherapy

Objective: Diabetes mellitus (DM) is a common comorbidity in patients with prostate cancer. Radiotherapy was reported to induce acute and late side effects in patients with DM due to vascular damage. Moreover, some studies have shown that metformin, an oral antidiabetic drug, can reduce biochemical and disease recurrence in patients with prostate cancer. This study aimed to evaluate retrospectively the effect of metformin on biochemical disease control and to observe the acute and late side effects of prostate cancer treated with radiotherapy. Materials and Methods: This study enrolled 94 patients who received radical radiotherapy between 2010 and 2017. However, out of 22 patients with DM, 17 received metformin and five received metformin plus insulin treatment. Biochemical recurrence-free survival (bRFS), overall survival, and side effects were assessed between patients with and without DM. Results: The median follow-up time was 57 (15-128) months. The 5-year bRFS rate in patients with and without DM were 100% and 89.2%, respectively (p=0.10). Acute grade 1-2 side effects were observed in all patients with DM, while 56 (78%) patients without DM had acute side effects, and the difference is significant (p=0.02). Acute grade 3 genitourinary and gastrointestinal toxicity was found in one patient without DM, whereas late grade 3 gastrointestinal toxicity was observed in one patient with DM. Conclusion: Although patients with DM were found to have better bRFS than patients without DM, we could not show the benefit of metformin, and the difference was not significant. By contrast, acute side effects were significantly higher in patients with DM.