Prospective Evaluation of FDG-PET/CT for On-treatment Assessment of Response to Neoadjuvant or Induction Chemotherapy in Invasive Bladder Cancer

BACKGROUND: Neoadjuvant/induction chemotherapy (NAIC) improves survival in patients with muscle-invasive bladder carcinoma (MIBC). On-treatment response assessment may aid in decisions to continue or cease NAIC. OBJECTIVE: We investigated whether 18F-fluoro-2-deoxy-D-glucose-Positron Emission Tomography/Computed Tomography (FDG-PET/CT) could predict response to NAIC and compared to contrast-enhanced Computed Tomography (CECT). METHODS: We prospectively included 83 patients treated for MIBC (i.e. high-risk cT2-4N0M0 or cT1-4N+M0-1a) between 2014 and 2018. Response to NAIC was assessed after 2-3 cycles with FDG-PET/CT (Peter-Mac and EORTC criteria) and CECT (RECIST1.1 criteria). We assessed prediction of complete pathological response (pCR; ypT0N0), complete pathological down-staging (pCD;≤ypT1N0), any down-staging from baseline (ypTN < cTN) and progression (inoperable tumor/ypN+/M+). The reference standard was histopathological assessment or clinical follow-up. Sensitivity, specificity, and accuracy were calculated. RESULTS: Pathological response rates were 21% for pCR, 29% for pCD, and 10% progressed. All patients underwent FDG-PET/CT and 61 patients also underwent CECT (73%). Accuracy of FDG-PET/CT for prediction of pCR, pCD, and progression were 73%, 48%, and 73%, respectively. Accuracy of CECT for prediction of pCR, pCD, and progression were 78%, 65%, and 67%, respectively. Specificity of CECT was significantly higher than FDG-PET/CT for prediction of pCD and any down-staging (p = 0.007 and p = 0.022). In all other analyses, no significant differences between FDG-PET/CT and CECT were found. CONCLUSIONS: Routine FDG-PET/CT has insufficient predictive power to aid in response assessment compared to CECT.