FDG PET-CT imaging in assessing interim response to neoadjuvant cisplatin-based chemotherapy (NAC) in muscle invasive bladder cancer (MIBC): A prospective study.

460 Background: Muscle invasive bladder cancer (MIBC) is an aggressive local disease where initial staging with conventional CT imaging is often suboptimal. To explore the role of PET-CT in both staging MIBC and assessing response to neoadjuvant chemotherapy (NAC), we conducted a prospective multicentre, randomized trial known as PETMUSE. We report here the first results from the neoadjuvant substudy which assessed interim PET-CT response after 2-3 cycles of NAC and how this correlated with disease free survival (DFS) and overall survival (OS). Methods: Patients with MIBC (T2a-4a, N0-3, M0) based on transurethral resection of their bladder tumor and CT staging were randomized 2:1 to PET-CT or no PET-CT. All PET-CT patients, receiving cisplatin-based NAC underwent a second PET-CT after 2 cycles of gemcitabine and cisplatin (GC) or 3 cycles of dose dense methotrexate, vinblastine, adriamycin, cisplatin (ddMVAC) to assess for interim response. Patients were scored (1-5) by 2 independent reviewers according to the extent of metabolic response on PET-CT. Disease-free survival (DFS) and overall survival (OS) were collected. Results: Between 2016 and 2021, 291 patients were enrolled on PETMUSE of which 46 participated in the neoadjuvant substudy. Median age was 68 (51-86); 36 (78%) were male; 26 were ECOG 0 (57%); 31 (68%) were T2, 13 (28%) were T3/T4; and 35 (76%) were node negative. In terms of NAC regimens: 22 (48%) received GC, 17 (37%) split dose GC, 6 (13%) ddMVAC, and 1 (2%) MVAC. On PET-CT, 23 (50%) had a complete metabolic response, 14 (30%) had a partial metabolic response, 5 (11%) had no change or mixed response and 4 (9%) had progressive disease or new lesion on PET scan. Metabolic response on PET-CT was a statistically significant prognostic factor for both DFS and OS (see Table). Conclusions: In MIBC patients receiving cisplatin-based NAC, metabolic response seen on interim PET-CT was correlated with DFS and OS. PET-CT warrants further study in this setting as a potential early indicator of response to NAC. Clinical trial information: NCT02462239 . [Table: see text][Table: see text]