AUA 2022: Robot-Assisted PSMA-radioguided Salvage Surgery in Recurrent Prostate Cancer Using a DROP-IN Gamma Probe - a Prospective Feasibility Study

( In a podium presentation at the 2022 American Urologic Association Annual Meeting held in New Orleans and virtually, Dr. de Barros presented preliminary data regarding the feasibility of robotic-assisted, Prostate-Specific Membrane Antigen (PSMA)-targeted radio-guided salvage surgery. The use of intraoperative PSMA-targeted radio guidance has been shown to be valuable for the detection of recurrent prostate cancer lesions during open salvage surgery.

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However, much prostate cancer surgery is now performed robotically. Thus, there is an increasing need to make PSMA-radioguided surgery (RGS) robot compliant. In this presentation, Dr. de Barros presented results of a miniaturized DROP-IN gamma probe to facilitate translation of PSMA-targeted radioguidance to salvage robotic surgery in men with recurrent prostate cancer.

The authors performed this prospective feasibility study (NCT03857113) among twenty patients with biochemical recurrence (PSA ≥ 0.2 ng/ml) after radical prostatectomy or radiotherapy. Patients could have up to 3 pelvic prostate cancer recurrences (either nodal or local) on PSMA positron emission tomography (PET)/CT.

Patients received an intravenous injection of 99mTc-PSMA I&S (median activity 541 MBq, IQR 526-578) one day prior to surgery followed by scintigraphy as a control for tracer injection and distribution. Robot-assisted PSMA-RGS was performed using a tethered gamma probe 19-23 hours post-injection.

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The authors sought to assess the primary endpoint of the feasibility of PSMA-RGS in a robotic setting. Secondarily, the authors performed a comparison of the radioactive status (i.e., positive or negative) of the resected specimens and final histopathology results, the frequency of >50% prostate-specific antigen (PSA) reduction, complete biochemical response (cBR; PSA <0.2 ng/ml) 6 weeks postoperatively, and complications according to Clavien-Dindo 30 days postoperatively.

At the time of surgery, the median age of included patients was 68 years (IQR 66-72) and median PSA was 1.02 ng/ml (IQR 0.46-2.43). Using the DROP-IN probe, 19 out of 21 (90%) PSMA PET-avid lesions could be resected robotically with a median surgical duration of 128 min (IQR 103-157). The signal to background noise ratio was favourable in both in-vivo and ex-vivo assessment.

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All benign specimens were not radioactive though there were 3 false negative results, though each of these had <2.6mm of tumor. On a per-lesion basis, the overall diagnostic sensitivity and specificity of robot-assisted PSMA-RGS was 86% and 100%, respectively. A PSA reduction of 50% or greater was seen in 12 out of 18 (67%) patients and complete biochemical response (PSA <0.2 ng/mL) was seen in 4 out of 18 (22%) patients. No Clavien-Dindo grade ≥2 complications occurred related to this portion of the procedure though there was one Grade 5 event.

The authors concluded that the DROP-IN probe allows for robot-assisted PSMA-RGS.

Presented by: Hilda De Barros, MD, MSC – Netherlands Cancer Institute

Written by: Christopher J.D. Wallis, University of Toronto, Twitter: @WallisCJD during the 2022 American Urological Association (AUA) Annual Meeting, New Orleans, LA, Fri, May 13 – Mon, May 16, 2022.


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