Abstract LB036: Clinical value of 18F-FDG-PET compared with CT scan in the detection of nodal and distant metastasis in urothelial carcinoma or bladder cancer
Authors: Oey Oliver , Viswambaram Pravin , Ong Jeremy , Gauci Richard , Low Ronny , Hayne Dickon 
Published: July 2021

Abstract
Computed tomography (CT) scan is the standard imaging modality for staging patients with urothelial carcinoma (UC) or bladder cancer (BC). Despite negative staging prior to surgery, 20-30% of patients have lymph node (LN) metastasis. Surgery for BC and UC has high morbidity and preoperative staging is vital. Value of 18F-fluorodeoxyglucose positron emission tomography (18F-FDG-PET) in staging UC and BC is debatable. We report a large series comparing 18F-FDG-PET with CT. We retrospectively reviewed 90 patients diagnosed with UC or BC who underwent surgery or confirmatory biopsy that were staged with both CT and 18F-FDG-PET between 2015 and 2020. 78 patients staged with CT and 18F-FDG-PET had formal pelvic LN dissection. 21 patients had neoadjuvant chemotherapy (NAC). 18F-FDG-PET reports for positive sites were qualitative, with 18F-FDG avid sites considered positive. On CT, enlarged LN by RECIST criteria 1.1 (&gt;10 mm) and other qualitative findings suggesting metastasis were considered positive. Histopathological findings from surgical specimens or image guided biopsy were considered gold standard in comparison to imaging reports. 18F-FDG-avid or enlarged pelvic LNs with surgically proven nodal metastasis were considered true positives. Performance characteristics of 18F-FDG-PET and CT including sensitivity, specificity, positive predictive value (PPV) and negative predictive value (PPV) were calculated. Metastatic pelvic LN were confirmed histologically in 18/78 (23.1%) patients. Sensitivity, specificity, PPV and NPV of CT for detecting pelvic LN metastases were 27.8% (95% CI:10.7-53.6%), 96.7% (95% CI:87.5-99.4%), 71.4% (95% CI:30.3-94.9%) and 81.7% (95% CI:70.4-89.5%) respectively. Sensitivity, specificity, PPV and NPV of 18F-FDG-PET for detecting pelvic LN metastases were 50.0% (95% CI:26.8-73.2%), 88.3% (95% CI:76.8-94.8%), 56.3% (95% CI:30.6-79.2%) and 85.5% (95% CI:73.7-92.7%) respectively. 11/90 (12.2%) patients had 18F-FDG-PET suggestive of distant metastases. 10 (90.9%) of these 11 patients had image guided biopsy of these 18F-FDG-PET-positive sites confirming metastases. Pre-operative staging with 18F-FDG-PET identified metastatic disease in 4/85 (4.7%) patients which were occult on CT. This retrospective study suggested that 18F-FDG-PET may be more sensitive than CT for detecting pelvic LN metastases. 4/85 (4.7%) patients avoided cystectomy due to 18F-FDG-PET diagnosed metastases which were not reported on CT. Further research involving randomised controlled trials comparing the diagnostic yield of 18F-FDG-PET and CT in detecting nodal and distant metastasis in UC or BC is warranted to confirm our findings.
Citation Format: Oliver Oey, Pravin Viswambaram, Jeremy Ong, Richard Gauci, Ronny Low, Dickon Hayne. Clinical value of 18F-FDG-PET compared with CT scan in the detection of nodal and distant metastasis in urothelial carcinoma or bladder cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB036.