However, while PSMA/PET CT is the latest functional imaging modality to be assessed, it is not the first. Other functional imaging studies including 11C-choline-PET/CT, 18F-Fluciclovine PET/CT, amongst others. Yet, while all have been compared to standard staging studies (CT A/P and NM Bone Scan), direct comparisons of these modalities are still being presented.
The authors of this abstract note that, despite their high specificity, PET/CT scan is limited by relatively low sensitivity at an individual lesion-level analysis in the context of recurrent prostate cancer (PCa). Moreover, the underestimation of tumor burden may be related to the extent of tracer uptake. They, therefore, hypothesized that under-estimation of tumor burden varies significantly according to PET/CT tracer by PSA level at salvage lymph node dissection (SLND). In this abstract, the authors specifically focus on PSMA PET/CT and 11C-choline PET/CT.
- Bilateral extended SLND was reported by all centers
Full demographics of both cohorts are shown below:
Median PSA at SLND was 2.3 ng/ml – slightly lower in the PSMA group (1.9) than Choline (2.5) (p < 0.05). Number of positive spots at pre-operative PET/CT scan was 1 in 320 (50%), 2 in 144 (22%), and 3+ in 177 (28%) patients, respectively. Median number of nodes removed at SLND was 22 (IQR: 15, 35). Number of positive nodes was 0 in 85 (13%), 1 in 137 (21%), 2 in 83 (13%), and 3+ in 336 (52%) patients, respectively.
Median under-estimation of tumour burden was 1. At MVA, 11C-choline was associated with a higher risk of under-estimation of tumour burden compared to 68Ga-PSMA (linear coefficient: 1.61; p < 0.0001). 11C-Choline showed a higher under-estimation at lower PSA levels when compared to 68Ga-PSMA (p < 0.0001). However, diagnostic accuracy of the two tracers became similar when PSA level exceeded 3 ng/ml (Figure 1).
Regardless, both imaging tools underestimated tumor burden more when there were more positive spots – so, in higher tumor burden patients, they underestimated nodal volume even more!
Based on these results, it would appear that 11C-choline under-estimates PCa tumour burden more compared to 68Ga-PSMA, and in particular, when the PSA < 1.5 and the number of positive spots <= 3 (low volume). However, the two tracers showed the same diagnostic accuracy in detecting nodal metastases when PSA exceeds 1.5 ng/ml. Yet, as these higher levels, standard staging studies may be able to accurately identified these nodal metastases and PET/CT may not be warranted. As this wasn’t assessed, it is unclear if PET/CT is needed at higher PSA levels.
Given a choice, however, there is increasing evidence that PSMA PET/CT may be superior to other PET/CT modalities, particularly at lower PSA levels and lower volume disease. But, if the decision is made to proceed with salvage lymph node dissection, extended bilateral node dissection is warranted due to underestimation of both imaging modalities.
Presented by: Nicola Fossati, MD, Università Vita-Salute San Raffaele; Urological Research Institute; San Raffaele Turro Hospital
Co-Authors:Carlo Andrea Bravi, Nazareno Suardi, Giorgio Gandaglia, Luca Boeri, R. Jeffrey Karnes, Axel Heidenreich, Alexander Kretschmer, Alexander Buchner, Christian Stief, Antonino Battaglia, Steven Joniau, Hein Van Poppel, Almut Kalz, Daniar Osmonov, Klaus-Peter Juenemann, Shahrokh Shariat, Bernhard Grubmüller, Andreas Hiester, Alessandro Nini, Peter Albers, Derya Tilki, Markus Graefen, Akbar Ashrafi, Inderbir S. Gill, Alexander Mottrie, Francesco Montorsi, Alberto Briganti
Written by: Thenappan Chandrasekar, MD (Clinical Instructor, Thomas Jefferson University) (twitter: @tchandra_uromd, @JEFFUrology) at the American Urological Association's 2019 Annual Meeting (AUA 2019), May 3 – 6, 2019 in Chicago, Illinois