Assessing Bladder Cancer Risk in Type 2 Diabetes Clinical Trials: the Dapagliflozin Drug Development Program as a 'Case Study'

Introduction: Dapagliflozin, a sodium-glucose co-transporter 2 inhibitor, decreases plasma glucose levels by suppressing renal glucose reabsorption and increasing urinary glucose excretion. Previously published pre-clinical data suggest that dapagliflozin lacks carcinogenic potential. This article reviews data on bladder cancer with dapagliflozin to illustrate the challenges in assessing bladder cancer in drug development programs in patients with type 2 diabetes mellitus (T2DM).

Methods: Clinical cases of bladder cancer were analyzed in a pooled population of >9000 patients in 21 phase 2b/3 dapagliflozin clinical trials of up to 208 weeks' duration.

Results: In the 21-study pool, demographic and baseline characteristics were generally consistent between dapagliflozin and comparator groups. The overall incidence of malignancies was also balanced between the treatment groups, with an incidence rate ratio (IRR) of 1.035 [95% confidence interval (CI): 0.724, 1.481]. Nine of 5936 dapagliflozin-treated patients and 1 of 3403 comparator-treated patients reported bladder cancer, with an IRR of 5.168 (95% CI: 0.677, 233.55). All of these patients had clinical attributes typical of bladder cancer in the general population (≥60-year-old males; 8 of the 10 patients were current/former smokers). All cases of bladder cancer were reported within 2 years of starting study treatment. There was an absence of detailed workup of hematuria prior to randomization, and no hematuria workup data were collected proactively in the dapagliflozin trials, which is typical of clinical practice. Failure to exclude bladder cancer prior to randomization increases the chance of recruiting patients with pre-existing bladder cancer in clinical trials and may delay the final diagnosis. Of the nine dapagliflozin-treated patients with bladder cancer, eight had microscopic hematuria prior to start of treatment or within 6 months of initiating study treatment.

Conclusion: The assessment of bladder cancer data illustrates the challenges of characterizing cancer risk in T2DM drug development programs. The totality of evidence to date does not suggest a causal relationship between dapagliflozin and bladder cancer.

Funding: AstraZeneca.