AUA 2017: 11C-Choline versus 68ga-PSMA PET/CT scan for the detection of nodal recurrence from prostate cancer: results from a large, multi-institutional salvage lymph node dissection series

Boston, MA (UroToday.com) This was a retrospective study that evaluated the diagnostic accuracy of PET/CT using either 11C-choline or 68Ga-PSMA in the setting of post-prostatectomy biochemical recurrence and imaging-detected lymphadenopathy treated with salvage lymph node dissection. The study retrospectively identified 266 patients affected by a single nodal recurrence and treated with SLND at eight tertiary referral centers. 74% had undergone 11C-choline and 26% had undergone 68Ga-PSMA ligand PET-CT.

The study outcomes were: (i) rate of negative histologic report at final pathology; (ii) concordance between site of positive imaging and location of positive nodes (iii) biochemical response (BR) defined as PSA ≤0.2 ng/ml at one month after SLND.

The two groups were fairly similar with regards to important variables that might affect the outcome. PSA levels were slightly lower in patients diagnosed with PSMA-ligand (2.2 vs. 1.5 ng/ml, p=0.011). The median number of lymph nodes removed was not significantly different (18 vs. 16, p=0.3). Overall, 50 (26%) patients diagnosed with 11C-choline and 19 (27%) patients diagnosed with PSMA had negative histologic report at final pathology (p=0.7), whereas 92 (47%) and 20 (30%) patients had ≥2 positive nodes, respectively (p=0.013). The concordance between site of positive imaging and location of positive nodes was not significantly different between groups (72% vs. 69%, p=0.3). 0verall, 93 (47%) and 23 (32%) patients had positive nodes outside the positive sites of PET/CT scan for 11C-choline v PMSA respectively (p=0.013). The biochemical response rate was significantly higher in the PSMA group (33% vs. 43%, p=0.016).

Clearly, these imaging modalities are not perfect. False positive rates (negative histology) were over 25%, and false negative rates were 30-47%. PSMA may appear slightly better, but improvement is still needed prior to routine clinical use. More information regarding whether patients with negative histology (but positive scans) were the patients with PSA persistence post-op would help the reader understand if this phenomena is more likely sampling/processing false negative vs false positive of the imaging study. 

Dr. Catalona made a very thoughtful comment that PSMA is not FDA-approved in the US and that we will depend on our European colleagues to continue these important studies to investigate the sensitivity of these studies. This is especially important for the many prostate cancer patients with BCR who would prefer to undergo salvage local therapy only if distant metastases have been effectively ruled out.

Presented by: Nicola Fossati, Milan Italy

Written by: Jed Ferguson, MD/PhD and Ashish Kamat, MD. MD Anderson Cancer Center, Department of Urology









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