Assessing the Performance of 18F-FDG PET/CT in Bladder Cancer: A Narrative Review of Current Evidence

Abstract

Introduction: Lymph node (LN) involvement is a crucial determinant of prognosis for patients with bladder cancer, and an accurate staging is of utmost importance to better identify timely and appropriate therapeutic strategies. To improve the accuracy of LN detection, as an alternative to traditional methods such as CT or MRI, 18F-FDG PET/CT has been increasingly used. 18F-FDG PET/CT is also used in post-treatment restaging after neoadjuvant chemotherapy. The aim of this narrative literature review is to provide an overview of the current evidence on the use of 18F-FDG PET/CT in the diagnosis, staging, and restaging of bladder cancer, with a particular focus on its sensitivity and specificity for the detection of LN metastasis. We aim to provide clinicians with a better understanding of 18F-FDG PET/CT's potential benefits and limitations in clinical practice.

Materials and methods: We designed a narrative review starting from a wide search in the PubMed/MEDLINE and Embase databases, selecting full-text English articles that have examined the sensibility and specificity of PET/CT for nodal staging or restaging after neoadjuvant therapy in patients with bladder cancer. The extracted data were analyzed and synthesized using a narrative synthesis approach. The results are presented in a tabular format, with a summary of the main findings of each study.

Results: Twenty-three studies met the inclusion criteria: fourteen studies evaluated 18F-FDG PET/CT for nodal staging, six studies examined its accuracy for restaging after neoadjuvant therapy, and three studies evaluated both applications. To date, the use of F-18 FDG PET/TC for detection of LN metastasis in bladder cancer is controversial and uncertain: some studies showed low accuracy rates, but over the years other studies have reported evidence of high sensitivity and specificity.

Conclusions: 18F-FDG PET/CT provides important incremental staging and restaging information that can potentially influence clinical management in MIBC patients. Standardization and development of a scoring system are necessary for its wider adoption. Well-designed randomized controlled trials in larger populations are necessary to provide consistent recommendations and consolidate the role of 18F-FDG PET/CT in the management of bladder cancer patients.

Keywords: FDG PET/CT; bladder cancer; lymph node; restaging; staging.

Figure 1

Example of a Radar Chart for the Proposed Bladder Cancer Scoring System. This chart represents an illustrative application of the proposed scoring system. Each axis corresponds to a parameter of the scoring system: standardized uptake values (SUVs), primary tumor size, lymph node involvement, and post-neoadjuvant chemotherapy (NAC) changes. The value along each axis represents the score for that parameter. SUVs is assigned as follows: 1 if SUV ≤ 2.5, indicating low metabolic activity and potentially less aggressive disease; 2 if 2.5 < SUV ≤ 5.0, suggesting moderate metabolic activity; 3 if 5.0 < SUV ≤ 7.5, suggesting relatively higher metabolic activity; 4 if 7.5 < SUV ≤ 10.0, indicative of high metabolic activity; 5 if SUV > 10.0, indicative of extremely high metabolic activity and potentially more aggressive disease. Primary tumor size is defined as follows: 1 if tumor size ≤ 2 cm, considered a small tumor; 2 if 2 cm < tumor size ≤ 4 cm, considered a moderately sized tumor; 3 if 4 cm < tumor size ≤ 6 cm, considered a relatively larger tumor, 4 if 6 cm < tumor size ≤ 8 cm, considered a large tumor, 5 if tumor size > 8 cm, considered a very large tumor, often associated with a worse prognosis. Lymph Node Involvement is defined as follows: 1 in case of no lymph nodes involved; 2 in case of single lymph node involvement; 3 in case of 2–3 lymph nodes involved, 4 in case of 4–6 lymph nodes involved, 5 in case of more than 6 lymph nodes involved, indicating extensive disease spread. Post-Neoadjuvant Chemotherapy (NAC) Changes are summarized as follows: 1 in case of no reduction in tumor size post-NAC, indicating no response; 2 in case of 1–25% reduction in tumor size post-NAC, suggesting a minimal response; 3 in case of 25–50% reduction in tumor size post-NAC, indicative of a partial response; 4 in case of 50–75% reduction in tumor size post-NAC, indicating a good response; 5 in case of more than 75% reduction or complete disappearance of the tumor post-NAC, indicating an excellent response. In this instance, hypothetical values are used for demonstration purposes: SUVs (4), Tumor Size (3), Lymph Node Involvement (4), and Post-NAC Changes (5). The filled area in the chart represents the composite score profile for a patient, providing a visual summary of the tumor’s characteristics according to the scoring system. Please note that in an actual case, values would be derived from clinical and imaging data, not randomly assigned.