In this first Major Observation, Dr. Graefen discussed the role of PSMA (Prostate specific membrane antigen) guided surgery for metastatic lymph nodes in prostate cancer.
He focuses on the series by Rauscher et al,1 in which they pretreat patients with technetium-111 1-day prior to surgery. They then tracked the tissue intra-operatively during their salvage lymphadenectomy for recurrent prostate cancer. They went on to correlate resected tissue and histolopathologic results. More importantly, they also determined the efficacy (PSA response without additional therapy).
Specifically, these are patients with recurrence after local definitive therapy (radiation or surgery). With low PSA levels, they often get PSMA PET scans now. Some are found to have oligometastatic disease in the pelvis that may be amenable to resection. In these patients, the authors pre-treated patients with the agent 1-day before surgery. Intra-operatively, similar to a sentinel lymph node dissection for breast cancer, they can track the signal based on counts of the technetium using a sterile probe. The tissue can be histologic evaluated once outside the body to confirm the presence of the tracked molecule – this can be recorded in the absence of background noise and serves as rapid confirmation of accurate resection.
In the initial study, they had 31 patients. In a recent update pending publication, they are up to 120 patients. These patients had a pre-salvage PSA of 1.3; 93% had primary surgery but 70% of these had some secondary therapy (radition, hormones, or combination). They then went on to compare ex-vivo radioactivity with histopathologic findings. They also determined PSA response without any planned adjuvant therapy, treatment-free survival, and complications.
In terms of results, 30/31 lesions were detected using gamma probe. 145 lesions removed, with 51 histologically proven metastatic sites. In ex vivo analysis, 48 were accurately identified as metastatic lesions. It correctly identified 87 of the negative lesions, but had 4 false negatives and 6 false positives. Test characteristics: 92% sensitivity, 94% specificity, Accuracy 93%, PPV 89%, NPV 96%.
Looking at best PSA response – 29 patients had good PSA respone. PSA reduction >50% was seen in 70% of patients. PSA response >90% was seen in 53% of patients. 60% had a PSA <0.2. PSA response was not seen in just 2 patients. 33% went on to additional treatment @ 125 days. 67% however had no additional treatment over the next year. In terms of complications, 4 patients (13%) had Grade 3 complications.
Take-home messages:
- High value of PSMA in Radio-guided surgery (RGS) to identify small metastatic sites
- RGS may be even more precise than PSMA PET scan – it identified 5 lesions not picked up on PSMA PET
- Promising short term outcomes with acceptable morbidity profile
- Patients must be well selected
References:
1 Value of 111In-prostate-specific membrane antigen (PSMA)-radioguided surgery for salvage lymphadenectomy in recurrent prostate cancer: correlation with histopathology and clinical follow-up. Rauscher I, Düwel C, Wirtz M, Schottelius M, Wester HJ, Schwamborn K, Haller B, Schwaiger M, Gschwend JE, Eiber M, Maurer T. BJU Int. 2017 Jul;120(1):40-47. doi: 10.1111/bju.13713. Epub 2016 Dec 4.
Presented by: Markus Graefen
Written by: Thenappan Chandrasekar, MD, Clinical Fellow, University of Toronto, Twitter: @tchandra_uromd at the 37th Congress of Société Internationale d’Urologie - October 19-22, 2017- Lisbon, Portugal