V11-02: 99m-Technetium-PSMA Radio-Guided Surgery to Detect Nodal Metastases in Prostate Cancer Patients Undergoing Radical Prostatectomy and Extended Pelvic Lymph Node Dissection: a phase 2 prospective, single-institution study

Giorgio Gandaglia*, Elio Mazzone, Antony Pellegrino, Milano, Italy, Nicola Fossati, Lugano, Switzerland, Armando Stabile, Francesco Barletta, Simone Scuderi, Riccardo Leni, Daniele Robesti, Lucia D’Ambrosio, Luca Maria Vitale, Ana Maria Samanes Gajate, Maria Picchio, Luigi Gianolli, Francesco Montorsi, Alberto Briganti, Milano, Italy

Introduction: An extended pelvic lymph node dissection (ePLND) is the gold standard for nodal staging in prostate cancer (PCa). Although PSMA PET has superior accuracy as compared to conventional imaging, its sensitivity for micrometastatic nodal metastases is suboptimal. Radioguided surgery (RGS) with 99m-Technetium-PSMA (99mTc-PSMA) might identify lymph node invasion (LNI) in patients undergoing an ePLND at the time of robot-assisted radical prostatectomy (RARP).

Methods: This is a phase 2 prospective study (NCT04832958) which aims at enrolling 100 patients (cN0cM0) undergoing RARP with an ePLND with a risk of LNI >5% based on the Briganti nomogram. After Ethical Committee approval, a total of 10 patients have been enrolled and 6 patients underwent RARP with 99mTc-PSMA RGS. After signing the informed consent, all patients underwent 68Ga-PSMA PET/MRI (mean activity: 149 MBq). 99mTc-PSMA I&S was synthesized and administered intravenously the day before surgery (mean activity: 730 MBq). A drop-in gamma probe was used for in vivo intraoperative measurements to identify metastatic lesions (a count rate of at least twice as compared to the background) at the level of the pelvic nodal stations. All positive lesions have been excised. An anatomically defined ePLND was performed. Radioactive tissue was excised and compared with the histopathological analysis.

Results: Mean age and PSA were 69 years and 9.2 ng/ml. Overall, 2 (33%) patients had cT3 disease at DRE. Biopsy ISUP grade group was 4-5 in 5 (88%) patients. Median LNI risk was 40%. Overall, 4 (66%) and 3 (50%) patients had ECE and SVI at mpMRI. A total of 2 patients had an uptake at PSMA PET/CT at 68Ga-PSMA/MRI with 3 and 7 positive spots. 99mTc-PSMA SPECT and RGS detected positive nodes in both patients. No adverse events after the injection of the tracer or intraoperative complications were recorded. Mean operative time, blood loss, and length of stay were 200 min, 50 ml and 3 days. The ISUP grade group was 4-5 in 4 (80%) patients with pathologic data available (n=5) and 3 (60%) patients had LNI (mean number of nodes removed and positive nodes: 24 and 4). The rate of pT3b, and PSM were 40% and 40%. 68Ga-PSMA PET and 99mTc-PSMA RGS identified LNI the pelvic region in both patients. On a per patient level, the sensitivity and specificity of PSMA RGS for pelvic LNI was 100%. On a per region analysis, the sensitivity and specificity were 85 and 98%.

Conclusions: 99mTc-PSMA RGS is a safe procedure. Although this approach virtually identified all patients with pelvic LNI at ePLND, it is characterized by a suboptimal sensitivity at a per region level. The final results of this trial will allow to assess the role of 99mTc-PSMA RGS in nodal staging for newly diagnosed PCa.

Source of Funding: none