Abstract LB036: Clinical value of18F-FDG-PET compared with CT scan in the detection of nodal and distant metastasis in urothelial carcinoma or bladder cancer

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 (>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.