Background: Bladder cancer is the 7th cause of death from cancer in men and 10th in women. For metastatic patients, prognosis is poor with a median overall survival of 15 months that remained unchanged for the past 15 years. No standard second-line chemotherapy is available for patients who relapse. Acquired mutations leading to a deregulation of the PI3K/AKT/mTOR pathway have been reported in more than 40% of bladder cancers suggesting the use of the mTOR (mammalian target of rapamycin) signalling pathway as an attractive target for the treatment of urothelial tumors. Methods: The main objective of this study was to assess the efficacy of temsirolimus, an mTOR inhibitor that is already used for the treatment of renal cancers, in patients with recurrent or metastatic bladder cancer who already received a first line chemotherapy. Efficacy was measured in terms of non-progression of the disease at two months of treatment following the RECIST v1.1 criteria. Based on a two-stage optimal Simon’s design, a total of 15 non-progressions out of 51 eligible and assessable patients were required to claim efficacy. Patients were treated at a weekly dose of 25 mg until progression, unacceptable toxicities or withdrawal. Results: Fifty-four patients were enrolled in the study between November 2009 and July 2014 in seven French centres. At the end of the first stage, six patients out of 17 were progression-free at 2 months leading to the inclusion of additional 37 patients in the second stage of the study. Thirty-six patients were eligible and assessable for the primary efficacy endpoint. A total of 18 (50%) non-progressions were observed at 2 months. Among them, partial response was documented for two patients and stable disease for 16. Twenty-five related adverse events were observed in 19 (35.2%) of the patients. Conclusions: Our study is providing the first clinical evidence of a potential benefit of temsirolimus for the treatment of relapsed bladder cancers. Ancillary study is ongoing to investigate the mutational status of genes which are involved in the PI3K/AKT/mTOR signalling pathway in order to identify a predictive signature of response to temsirolimus in bladder cancer. Clinical trial information: NCT0187943NCT0187943.