PET in bladder cancer imaging

The aim of this study was to summarize the available evidence on different PET imaging modalities for the staging of patients diagnosed with bladder cancer (BCa). We further discuss the use of PET/computed tomography (CT) and PET/MRI with different radiopharmaceuticals to characterize tumour biology for treatment guidance.

Available evidence supports the benefits of PET/CT in BCa staging due to its higher accuracy in the detection of nodal metastases compared with CT alone. The use of PET/MRI is of major future interest due to the higher soft tissue contrast of MRI, which might enable the early detection of the tumour in the bladder. For the time being, the sensitivity of PET/MRI is still too low, when it comes to the diagnosis of early-stage BCa. This is mainly due to the renal excretion of the commonly used [ 18 F]FDG PET tracer, wherefore small lesions in the wall of the bladder can be missed. Novel studies using PET radiopharmaceuticals to target immune checkpoints or other immune cell targets (immunoPET) demonstrated high uptake in tumour lesions with high PD-L1 expression. The use of immunoPET could therefore help identify BCa patients who exhibit PD-L1 positive tumours for systemic immune-therapy.

PET/CT and PET/MRI seem to be promising imaging tools in BCa staging, especially for the detection of lymph node and distant metastases, as they are more accurate than conventional CT. Future clinical trials with novel radiopharmaceuticals and machine-learning driven PET-technologies bear the potential to help in the early detection, staging, monitoring and precision-medicine approach. Specifically, immunoPET is of high future interest, as it could help develop the concept of precision-medicine in the age of immunotherapy.