Benign prostate hyperplasia (BPH) may be a significant risk factor for bladder cancer among patients with type 2 diabetes, new findings suggest. Metformin may protect against bladder cancer in men with BPH.

Chin-Hsiao Tseng, MD, of National Taiwan University College of Medicine in Taipei, analyzed data from 547,584 men with type 2 diabetes. He followed patients from the study enrollment date of January 1, 2006, until the end of 2009.

The incidences of bladder cancer were 258.77 per 100,000 person-year for patients with BPH compared with 69.34 per 100,000 person-year for those without BPH, Dr. Tseng reported in BMC Cancer (2013;13:7) In adjusted analyses, men with BPH had a significant 79% increased likelihood of developing bladder cancer. Among the men with BPH, those who underwent surgical procedures for BPH had a higher incidence than those who did not (355.45 vs. 250.09 per 100,000 person-years. Compared with patients who did not have BPH, those who underwent surgery for BPH had a greater than twofold increased risk for bladder cancer and those who had BPH but did not undergo surgery had a 71% increased risk.

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In subjects with BPH, diabetes duration was not significantly related to bladder cancer, suggesting that the effect of BPH on bladder cancer is independent of diabetes. Metformin use was associated with a significant 28% decreased risk for men of all ages and a 26% decreased risk for men aged 60 years and older.

Dr. Tseng explained that residual urine in the bladder in BPH sufferers increases the contact time between urinary excreted carcinogens and the urothelium. “Therefore, theoretically, patients with BPH may have an increased risk of bladder cancer,” he stated.

With respect to the higher risk of bladder cancer among BPH sufferers who underwent surgery, Dr. Tseng noted that this suggests patients with more severe clinical conditions of BPH might have a higher risk of bladder cancer.

The researcher said his study has some important clinical implications. BPH-related bladder cancer can be preventable if BPH is prevented or adequately treated at its early stage. In addition, among diabetic men with BPH, the use of metformin potentially could prevent bladder cancer. “This finding surely provides a good rationale for the conduction of clinical trials evaluating the use of metformin for the prevention of bladder cancer among high-risk patients with BPH,” Dr. Tseng wrote.

Dr. Tseng noted that human studies exploring the link between BPH and bladder cancer remain sparse. Two early case-control studies suggested an elevated risk of bladder cancer in men with BPH. In addition, a cohort study of 79,280 Swedish men hospitalized for BPH from 1962 to 1983 and followed until 1989 found no overall increased risk of bladder cancer associated with BPH; however, patients who underwent transurethral resection of the prostate had a significant 47% increased risk.