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To the Editor Dr Lewis and colleagues1 reported that more than 4 years’ duration of pioglitazone use was not associated with a statistically significant increased risk of bladder cancer (hazard ratio, 1.22; 95% CI, 0.92-1.61) after adjusting for several covariates, including calendar year at cohort entry.
This result contrasts with their previous analysis,2 and an accumulating body of evidence from other trials and observational studies, which all support an increased risk of bladder cancer with pioglitazone.3 As a result, the International Agency for Research on Cancer classified pioglitazone as a probable human carcinogen (grade 2A).4
Singh S, Suchard MA. Pioglitazone Use and Risk of Bladder Cancer. JAMA. 2015;314(23):2567-2568. doi:10.1001/jama.2015.13912