The Future of PSMA PET and WB MRI as Next-Generation Imaging Tools in Prostate Cancer - Beyond the Abstract

Next generation imaging (NGI) such as PSMA PET and Whole-body MRI has been shown to increase the diagnostic accuracy for the staging of prostate cancer across the disease spectrum, compared to conventional imaging modalities such as CT and bone scan. In this article, we reviewed the current evidence for the use of PSMA PET and WB-MRI in various settings and how their limitations could affect clinical decision making.

PSMA PET-CT has been shown to have higher sensitivity and specificity in detecting nodal and bone metastatic lesions than conventional imaging, especially at low PSA levels. This helps with early detection of disease and has made PSMA PET useful in treatment planning, particularly during the primary staging and biochemical recurrence settings. PSMA PET derived quantitative biomarkers such as PSMA derived tumour volume and total lesion PSMA give measures for whole body tumour burden, have good prognostic value, and can be used for assessment of treatment response. In addition to its uses in imaging, PSMA labelled ligands can act as radiotheranostics. For example, Lu-PSMA has been demonstrated to be a potential new treatment for metastatic castrate resistant prostate cancer. Standardised radiology reporting criteria or PSMA PET images such as PROMISE, PSMA-RADS, and E-PSMA have been proposed and applied in some clinical studies but not yet validated in large trials.

Whole body MRI is showing increasing promise as an 'all-in-one' modality for cancer diagnosis and staging without the need for radiation exposure. The Steamline C and Steamline L Trials have demonstrated that compared to conventional staging pathways, WB-MRI has higher sensitivity, requires less time to complete staging, and is more cost effective in settings of newly diagnosed colorectal cancer and non-small cell lung cancer (NSCLC), respectively. WB-MRI derived biomarkers such as apparent diffusion coefficient(ADC), signal fat fraction (sFF) and proton density fat fraction are especially useful in the assessment of bone metastases. Similar to PSMA-PET, criteria such as MET-RADS-P have been proposed to standardise reporting of WB-MRI.
The higher sensitivity of NGIs means that small lesions that would otherwise not be visible on conventional imaging may be detected on NGI, potentially resulting in ‘stage migration’. However, the clinical significance of these small lesions is unknown and clinical decisions based on those findings need to be carefully considered, as the upstaging and the consequent change in treatment focuses away from radical therapy could potentially deny patients a chance of cure.

While introducing NGIs into routine clinical practice is the step forward, larger randomised trials comparing the performance of PSMA PET and WB-MRI in prostate cancer are lacking. In the future, the outcomes of these trials should ideally include parameters that measure clinical benefit such as disease free survival and overall survival. Health economic analysis based on these data can be carried out and further inform healthcare service providers during implementation of NGIs.

Written by: Yishen Wang, Sola Adeleke, & Veeru Kasivisvanathan

  1. School of Clinical Medicine, University of Cambridge, Cambridge, UK
  2. Department of Oncology, University College London Hospitals, London, UK
  3. Division of Surgery & Interventional Science, University College London, London, UK

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