Pioglitazone, Bladder Cancer, and the Presumption of Innocence

Background: Thiazolidinediones are potent exogenous agonists of PPAR-γ that augment the effects of insulin to its cellular targets, mainly at the level of adipose tissue. Pioglitazone, the main thiazolidinedione in clinical practice, has shown cardiovascular and renal benefits in patients with type 2 diabetes, durable reduction of glycated hemoglobulin levels, important improvements of several components of the metabolic syndrome, and beneficial effects of non-alcoholic fatty liver disease. Objective: Despite all of its established advantages, the controversy for an increased risk of developing bladder cancer, combined with the advent of newer drug classes that achieved major cardiorenal effects, have significantly limited its use spreading a persistent shadow of doubt for its future role. Methods: Pubmed, Google, and Scope databases have been thoroughly searched, and relevant studies were selected. Results: This paper thoroughly explores both in vitro and in vivo (animal models and humans) studies that investigated the possible association of pioglitazone with bladder cancer. Conclusion: Currently, the association of pioglitazone with bladder cancer cannot be based on solid evidence. This evidence cannot justify its low clinical administration, especially in the present era of individualised treatment strategies. Definite clarification of this issue is imperative and urgently anticipated from future high quality and rigorous pharmacoepidemiologic research, keeping in mind its unique mechanism of action and its significant pleiotropic effects.