Background: Cisplatin-based chemotherapy remains the perioperative treatment in muscle-invasive bladder carcinoma (MIBC). Recent evidence suggests that immune checkpoint inhibitors could be incorporated in this setting. Olaparib is a PARP inhibitor with well-established activity in HRD tumor. Results from trials assessing the combination of durvalumab and olaparib suggest a synergistic effect. However, a molecular characterization is crucial to warrant a rational development. Methods: A phase II clinical trial was designed to assess the impact of neoadjuvant treatment with the combination of durvalumab plus olaparib in the molecular profile of MIBC (NCT03534492; SOGUG-2017-A-IEC(VEJ)-2). Efficacy and safety were secondary objectives. Subjects with cT2-T4a MIBC aimed for cystectomy were treated during 6 to 8 weeks pre-cystectomy. Diagnostic and surgical samples, pre and postreatment blood samples have been collected for the molecular analysis. We present results regarding efficacy and safety. Results: From November 2018 to October 2019 28 patients have been enrolled. 52%/48% of patients had PS 0/1. Median age was 70. TNM stage was: pT2 in 73,6% patients, pT3 in 10.6%, pT4 in 15.8% and 10.6% presented nodal spread. 13 patients have completed neoadjuvant treatment so far and 12 have undergone cystectomy. A wound dehiscence and one death related to surgical procedures were postoperative complications. Pathological complete response rate is 44,5%. Radiological evaluation is ongoing. 10 serious adverse events non-treatment related have been communicated. Any grade of toxicity has been reported in 91% of patients but adverse events grade 3-4 was detected in only 8.3% of cases. Grade 1 pruritus was the unique IR adverse event described in one patient. PARP inhibitors-related adverse events were grade 1 nausea and vomiting (25%), and grade 1 anemia (25%). Conclusions: Preliminary clinical data suggest that Durvalumab in combination with Olaparib could be active and well-tolerated neoadjuvant treatment of MIBC. Molecular characterization and biomarker discovery will be presented separately. Clinical trial information: NCT03534492