Diabetes mellitus (DM) appears to be an independent predictor of disease recurrence and progression among patients with non-muscle invasive bladder cancer (NMIBC), according to investigators.

In a retrospective study of 251 patients who underwent transurethral resection (TUR) for NMIBC, the 92 patients with DM at the time of surgery had a twofold and ninefold increased risk of disease recurrence and progression, respectively, compared with non-DM patients, after adjusting for multiple possible confounders, researchers reported in the International Journal of Urology (2011;18:769-776). The DM patients were older and had a higher rate of hypertension compared with the patients without diabetes.

Additionally, compared with patients who had a hemoglobin A1c level below 7%, those with high levels (representing poor glycemic control) had a significantly greater tumor multiplicity, more high-grade tumors, and received significantly more intravesical therapy.

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The investigators, led by Seung Il Jung, MD, and colleagues at Chonnam National University Medical School in Gwangju, Korea, concluded that “close follow-up and intravesical therapy may be beneficial in patients with DM, especially those with poor glycemic control.”

The mechanism by which DM contributes to bladder cancer is unclear. In a discussion of some of the possibilities, the researchers cited studies suggesting that chronic exposure to hyperinsulinemia or hyperglycemia induces tumor cell proliferation and metastasis, and that increased insulin-like growth factor in diabetic patients stimulates cellular proliferation and inhibits apoptosis. Furthermore, studies have demonstrated an association between diabetes and an increased risk of urinary tract infection (UTI), which has been related to bladder cancer risk, and UTI may affect the incidence of recurrence or progression, the authors observed.

The authors noted that their study is limited by its retrospective design, relatively small sample size, and by the low frequency of tumor recurrence and progression. The researchers also pointed out that they did not assess the duration of DM, which may have been affected by recall bias or a period of undetected DM.