INTRODUCTION AND OBJECTIVE:
The ability to accurately determine the location and extent of lymph node involvement has significant implications in the management of prostate cancer (PCa). Radioguided surgery has emerged as a promising means of assisting the detection of lymph node metastases at the time of radical prostatectomy (RP) and extended pelvic lymph node dissection (ePLND) in men with high-risk PCa due to the recent development of prostate-specific membrane antigen (PSMA) labelled with gamma-emitting radionuclides such as technetium-99m (99mTc). The DETECT trial is a prospective, international, multi-institutional study that aims to evaluate the feasibility and effectiveness of radioguided surgery in this setting using 99mTc-labelled PSMA targeting.
Men over the age of 18 with ≥cT3a or Gleason score ≥4+3=7 PCa, with suspected (Briganti nomogram risk >10%) or known lymph node metastasis, who have undergone a pre-operative PSMA PET scan were consented to undergo a pre-operative intravenous administration of 99mTc-labelled PSMA (500 MBq). Patients then underwent a robot-assisted RP with ePLND and had intraoperative measurements taken with a drop-in, in vivo gamma probe at template lymph node sites, the prostate, prostate bed and other sites suspected of harbouring prostate cancer. All patients underwent an ePLND as standard of care. Histopathological concordance with intraoperative gamma probe findings was evaluated to establish the accuracy of the probe in detecting prostate cancer metastases. This clinical trial has received institutional ethics approval.
A total of 10 patients were included in the study with a median age of 68 years (IQR, 63.3-69) and pre-operative PSA of 9.15 ng/ml (IQR 6.9-14). The majority of patients harboured ISUP Grade Group 5 disease (70%) and had avid lymph nodes on pre-operative PSMA PET (80%). In total, 61 extraprostatic tissue specimens were resected, of which 16 (26.2%) had histological evidence of prostate cancer. The sensitivity, specificity, negative and positive predictive values of the gamma probe in the intraoperative detection of extraprostatic prostate cancer was 68.8% (95% CI 41.3 - 89%), 82.2% (95% CI, 68 - 92%), 57.9% (95% CI 40.3 - 73.7%) and 88.1% (95% CI 77.9 - 93.9%) respectively. The intraoperative use of the drop-in gamma probe in conjunction with CT-guided hookwire localisation was notably effective in the surgically challenging dissection of PSMA-avid mesorectal lymph nodes in 2 patients. In 1 patient, the gamma probe identified residual disease at the prostate bed which was confirmed on histological analysis. Only 1 minor post-operative complication was observed with no complications greater than Clavien-Dindo Grade I seen in the immediate 8-week follow-up period.
Interim results from the DETECT trial show that the use of the 99mTc-PSMA targeting as valuable and safe in the detection of lymph node metastases and suspected residual disease.
Source of Funding:
This trial is funded by St Vincent's Prostate Cancer Centre