Accuracy of FDG-PET/CT for Response Evaluation of Muscle-Invasive Bladder Cancer following Neoadjuvant or Induction Chemotherapy

Introduction: The aim of the study was to confirm the diagnostic accuracy of a second FDG-PET/CT following neoadjuvant or induction chemotherapy (NAIC) prior to radical cystectomy for patients with localized muscle-invasive bladder cancer (MIBC). Methods: Retrospective review of 62 consecutive patients with MIBC, that had a first FDG-PET/CT between April 2016 and September 2021. Patients then underwent NAIC, followed by a second FDG-PET/CT and radical cystectomy. Patients with no hypermetabolism in the bladder and lymph nodes on the second FDG-PET/CT were considered metabolic complete responders, while patients with no evidence of residual disease on histopathology were considered pathologic complete responders. The accuracy of the second FDG-PET/CT to distinguish complete responders from patients with residual disease was calculated, with histopathology as gold standard. Results: Of 62 patients, 1 was lost to follow-up, 5 died before radical cystectomy, 5 had delay >2 months between the second FDG-PET/CT and radical cystectomy, and 6 did not undergo radical cystectomy and instead underwent alternative treatment. The study cohort comprised 45 patients, 39 males and 6 females, with an age of 66 +/- 6 years. In comparison to histopathology, FDG-PET/CT provided (i) sensitivity of 95% and specificity of 42%, for the overall disease; (ii) sensitivity of 100% and specificity of 36%, for the primary tumor only; and (iii) sensitivity of 97% and specificity of 30%, for the lymph nodes only. Conclusion: FDG-PET/CT has over 95% sensitivity for distinguishing complete responders from patients with residual disease. Thus, FDG-PET/CT can be used for early response evaluation following NAIC to identify patients that did not completely respond to chemotherapy and may require alternative treatment pathways.