SIU 2019 39th Annual Society of International Urology Congress

SIU 2019: PET Imaging in Renal Cell Carcinoma and Urothelial Cancers

Athens, Greece ( Dr. Eoin MacCraith continued the PET imaging session with a nice overview of the use of PET-FDG in renal cell carcinoma (RCC) and urothelial cancers. PET is beneficial in diagnostics, staging, prognostics, and assessing therapeutic response, but it is currently not recommended for routine use.

One of the earlier tracers used is the 18F-FDG which is highly expressed in aggressive tumors with its uptake regulated by glucose-1-transporter expression. Aggressive tumors are highly avid for glucose.

The role of PET FDG imaging for the diagnosis of RCC is limited as the tracers are excreted through the urinary system there is a high false negative, as the tracer can obscure the tumor.

The sensitivity of conventional CT vs. PET for detection of RCC is 91.7% vs. 60%.1 However, when comparing the accuracy of PET vs. CT for detecting distant metastases of RCC, PET is shown to be more accurate (94% vs. 89%).2 The sensitivity/accuracy for the detection of bone metastases when comparing bone scans to PET is 77.5%/59.6% vs. 100%/100%.3 The pooled sensitivity of PET for the detection of RCC is 50-60%.4 Higher FDG uptake correlates with higher stage and grade5 (Figure 1).

Promising results are reported when assessing the role of PET FDG in RCC recurrence. The sensitivity of PET FDG in this scenario is reported at 90%, specificity 91%, and an accuracy of 90%.6 Moreover, PET FDG was shown to alter management in 43% of metastatic/recurrent RCC lesions.7

Despite these favorable results, the routine use of PET-FDG is not recommended in RCC, but it may be beneficial when there is diagnostic uncertainty on conventional surveillance CT.

The metabolic quantitation in PET can be performed by measuring the maximum standardized uptake value (SUVmax). SUVmax on PET correlates with a poorer prognosis.8 In metastatic RCC treated with sunitinib, the SUVmax for PET at 16 weeks correlated with decreased survival.9 A partial metabolic response was associated with improved overall survival/progression-free survival. An important finding was that the highest survival rates were seen in patients with the greatest post-therapeutic reduction in SUVmax.10 This important finding may potentially mean that a change in FDG uptake may be a useful indicator of Tyrosine Kinase Inhibitor's response.

In the next part of this talk, Dr. MacCraith moved on to discuss the role of PET FDG imaging in urothelial cancer. It is quite similar to RCC, demonstrating a limited role, due to the fact that this tracer is excreted through the urine which can obscure present tumors (Figure 2). However, there are data showing that PET FDG has better sensitivity than conventional CT for detecting pelvic node metastases (57% vs. 33%).11 The pooled sensitivity of PET CT for staging/restaging in urothelial cancer is 89%.12 PET FDG detected more disease than CT in 40% of cases and altered management in 68% of cases.13 Positive PET is associated with higher disease progression and reduced overall survival. Despite these advantages, they have not resulted in issuing a recommendation to routinely use this imaging modality.

For upper tract urothelial carcinoma (UTUC), PET FDG has been shown to be superior to conventional CT for detecting distant metastases and significantly altering management.14 It has better overall survival and progression-free survival for patients who show a response on PET after 2 cycles of chemotherapy, but again, this has not been enough to recommend routine use.

The EAU guidelines to date state that there are insufficient data on the use of FDG-PET/CT in muscle-invasive bladder cancer to allow a recommendation to be made. For RCC the recommendations are quite the same, with the guidelines clearly stating to not routinely use bone scan and/or PET CT for RCC staging.

Final take-home messages of this talk included that these advanced imaging modalities are not to be routinely used in diagnosis or staging of RCC and urothelial cancer. These imaging modalities could be a useful adjunct in surveillance when conventional imaging is inconclusive and may potentially alter management. Lastly, there is some use of PET CT in assessing therapeutic responses to tyrosine kinase inhibitors in metastatic RCC.

Figure 1- PET CT in renal cell carcinoma - Fused coronal PET/CT (A) and fused sagittal PET/CT (B) show increased FDG uptake in the primary RCC tumor in the right kidney (solid arrow), in a right adrenal gland metastasis (semidotted arrow), mediastinal lymph node metastases (dotted arrow), and bone metastases (interrupted arrow). Furthermore, there was markedly increased linear FDG uptake in a massive tumor thrombus in a dilated inferior vena cava (asterisk).15


Figure 2- Urinary FDG excretion masking a bladder tumor. Axial fused FDG PET/CT image at standard windowing to an SUV max of 10 shows no obvious abnormality within the pelvis16


Presented by: Eoin MacCraith, Urology SpR, Department of Urology, Beaumont Hospital, Dublin, Ireland

Written by: Hanan Goldberg, MD, Urology Department, SUNY Upstate Medical University, Syracuse, New-York, USA @GoldbergHanan at the 39th Congress of the Société Internationale d'Urologie, SIU 2019, #SIUWorld #SIU2019, October 17-20, 2019, Athens, Greece


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