2361MO Impact of positron emission tomography (PET) imaging on staging of muscle-invasive bladder cancer (MIBC) [PET-MUSE]

In MIBC standard staging with CT imaging is critical for making treatment decisions about neoadjuvant chemotherapy (NAC), and local treatment with either radical cystectomy (RC) or chemoradiation. However, CT imaging can often underestimate disease extent. The aim of this randomized study was to determine if adding 18F-FDG PET/CT (PET) to baseline CT, changes treatment received. Newly diagnosed MIBC pts (T2a-T4, N0-3, M0) without metastases on baseline CT, and predominant urothelial histology, were allocated 2:1 to PET or no further imaging. Enrollment occurred 05/16-11/21 at 6 Ontario centers. At the time of analysis, median duration of follow-up was 2 years. Primary outcome was proportion of pts not receiving expected treatment and secondary outcomes were disease-free survival (DFS) and overall survival (OS). Of 292 pts, 194 were randomized to PET and 98 to no PET. In the PET and no PET arms respectively: median age was 70 (43-93) and 68 (42-89); T2: 77% and 77%; node negative 88% and 87%; planned RC 66% and 69%; and planned NAC 70% and 64%. On PET, primary bladder tumor was seen in 86 (47%) pts, positive pelvic lymph nodes in 37 (20%), distant nodes in 32 (18%) and distant metastases in 13 (7%). By ITT analysis, 166 (86%) PET pts received expected treatment, 21 (11%) did not and 7 (4%) withdrew/died prior to treatment. In the no PET arm, 90 (92%) received expected treatment, 4 (4%) did not, and 4 (4%) withdrew/died prior to treatment. More PET pts were deemed palliative 18 (9.3%) vs 3 (3.1%). Notably >60% in both arms received NAC. PET pts were more likely to have a change in treatment, odds ratio 2.89 (95% CI 0.96-8.74, p=0.06) compared to CT alone. No statistically significant difference was observed between arms for DFS (HR=0.78, 95% CI 0.55-1.12) or OS (HR=1.02, 95% CI 0.66-1.56). In this large randomized study, there was a trend towards a change in management in pts having a PET, but this did not reach statistical significance. This trial provides new insights into the clinical utility of PET-CT in MIBC.