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We studied diagnosis accuracy of 18 FDG-PET Computed Tomography (CT) in nodal staging of muscle invasive bladder cancer (MIBC) and the rate of treatment modification according to FDG-PET CT results. FDG-PET CT was more sensitive compared to CT alone for lymph node (LN) staging. Treatment decision were modified for 26% of patient due to FDG-PET CT findings. Introduction: Guidelines do not recommend FDG-PET CT for the staging of MIBC as a standard. The objectives of the study are to assess the accuracy of the FDG-PET CT for LN staging and to determine the rate of treatment modification according to FDG-PET CT results in MIBC. Patients and methods: From January 2005 to December 2017, we carried out a retrospective analysis of patients with MIBC who had a FDG-PET CT for staging in two expert centres in Bordeaux, France, and analyzed its clinical value in this setting. Nodal and metastatic staging on CT scan (CT) and FDG-PET CT were done independently. Results: Accuracy of LN staging from CT and FDG-PET CT at initial diagnosis was analyzed in 85 patients (including 70 patients treated with neoadjuvant chemotherapy (NAC)) and compared to pathological examination of resected LN. Sensitivity of FDG-PET CT was better than CT (80.8% versus 26.9%) but the specificity was low (54.2% vs. 83.1%). The Youden index was better for FDG-PET CT (0.35; 0.1 for CT) and FDG-PET CT appeared to be more accurate for determining LN staging of MIBC. FDG-PET CT findings enabled a treatment decision modification in 34/130 patients (26.1%): a therapeutic intensification (9.2%), including surgery not previously planned and/or modified fields of radiotherapy; or a de-escalation (16.9%), mostly avoiding surgery. Conclusion: FDG-PET CT was more sensitive for detection of LN involvement at initial diagnosis of MIBC than CT alone. In our study, treatment decisions were modified, according to FDG-PET CT results, in almost a quarter of patients. [ABSTRACT FROM AUTHOR]