Histological comparison between predictive value of preoperative 3-T multiparametric MRI and 68 Ga-PSMA PET/CT scan for pathological outcomes at radical prostatectomy and pelvic lymph node dissection for prostate cancer.

OBJECTIVE: To evaluate the ability of preoperative multiparametric magnetic resonance imaging (mpMRI) and a gallium-68 prostate-specific membrane antigen positron emission tomography/computed tomography (68 Ga-PSMA PET/CT) scan to predict pathological outcomes and also identify a group of men with a <5% risk of histological pelvic lymph node metastasis (LNM) at pelvic lymph node dissection (PLND) performed during a robot-assisted laparoscopic radical prostatectomy (RALP) for prostate cancer. We then aimed to compare these results to known risk calculators for LNM, including the Cancer of the Prostate Risk Assessment (CAPRA) score, Memorial Sloan Kettering Cancer Centre (MSKCC) and Briganti nomograms. PATIENTS AND METHODS: Between July 2014 and September 2019 only men who had both a preoperative mpMRI and staging 68 Ga-PSMA PET/CT at our institution followed by a RALP with PLND referred to a single specialist uropathology laboratory were considered for inclusion. The data were collected retrospectively prior to February 2019 and in a prospective manner thereafter. A model was built to allocate probabilities of the men with a negative 68 Ga-PSMA PET/CT scan having a <5% risk of histologically LNM at RALP based on the preoperative radiological staging. RESULTS: A total of 233 consecutive men met the inclusion criteria of which 58 men (24.9%) had a LNM identified on PLND histology. The median (range) International Society of Urological Pathology (ISUP) Grade was 5 (1-5) and the median (range) prostate-specific antigen level was 7.4 (1.5-72) ng/mL. The median (range) number of resected lymph nodes was 16 (1-53) and the median (range) number of positive nodes identified on histology was 2 (1-22). Seminal vesicle invasion on mpMRI was more common in node-positive men than in the absence of LNM (31% vs 12%). The maximum standardised uptake value of the primary tumour on 68 Ga-PSMA PET/CT was higher in men with LNM (median 9.2 vs 7.2, P = 0.02). Suspected LNM were identified in 42/233 (18.0%) men with 68 Ga-PSMA PET/CT compared with 22/233 (9.4%) men with mpMRI (P = 0.023). The positive and negative predictive value for 68 Ga-PSMA PET/CT was 66.7% and 84.3% respectively, compared to 59.1% and 78.7% for mpMRI. A predictive model showed only two men (4.2%) with a negative preoperative 68 Ga-PSMA PET/CT would be positive for a histological LNM if they are ISUP Grade < 5 and Prostate Imaging-Reporting and Data System (PI-RADS) <5; or ISUP Grade 5 with PI-RADS < 4. An inspection of three additional variables: CAPRA score, MSKCC and Briganti nomograms did not improve the predictive probability for this group. However, of the 61 men with ISUP Grade 4-5 malignancy and also a PI-RADS 5 mpMRI, 20 (32.8%) men had a microscopic LNM despite a negative preoperative 68 Ga-PSMA PET/CT. CONCLUSION: Preoperative 68 Ga-PSMA/PET CT was more sensitive in identifying histological pelvic LNM than 3-T mpMRI. Men with a negative 68 Ga-PSMA PET/CT have a lower risk of LNM than predicted with CAPRA scores or MSKCC and Briganti nomograms. We identified that the combination of a negative preoperative 68 Ga-PSMA PET/CT, ISUP biopsy Grade <5 and PI-RADS <5 prostate mpMRI, or an ISUP Grade 5 with PI-RADS <4 on mpMRI was associated with a <5% risk of a LNM. The addition of CAPRA scores, MSKCC and Briganti nomograms did not improve the predictive probability within this model. Conversely, men with ISUP Grade 4-5 malignancy associated with a PI-RADS 5 prostate mpMRI had a >30% risk of microscopic LNM despite a negative preoperative 68 Ga-PSMA PET/CT and this high-risk group would appear suitable for an extended PLND at the time of a radical prostatectomy.

Risk of metastatic disease on 68 gallium-prostate-specific membrane antigen positron emission tomography/computed tomography scan for primary staging of 1253 men at the diagnosis of prostate cancer.

OBJECTIVE: To determine the number of men with 68 gallium-prostate-specific membrane antigen positron emission tomography/computed tomography (68 Ga-PSMA PET/CT) avid metastasis at diagnosis, as most data on 68 Ga-PSMA PET/CT are for the evaluation of recurrent disease after primary treatment and to our knowledge this study is the largest series of primary prostate cancer staging with 68 Ga-PSMA PET/CT. PATIENTS AND METHODS: A retrospective review conducted on 1253 consecutive men referred by urologists or radiation oncologists to our tertiary referral centre for 68 Ga-PSMA PET/CT scan for staging at the initial diagnosis of prostate cancer between July 2014 and June 2018. The primary outcome measure was to determine the risk of metastasis based on 68 Ga-PSMA PET/CT. Patients were risk stratified based on histological biopsy International Society of Urological Pathology (ISUP) grade, prostate-specific antigen (PSA) level, and staging with pre-biopsy multiparametric magnetic resonance imaging (mpMRI). Univariate and multivariate logistic regression were used to analyse results. RESULTS: The median PSA level was 6.5 ng/mL and median ISUP grade was 3, with high-risk disease in 49.7%. The prostate primary was PSMA avid in 91.7% of men. Metastatic disease was identified in 12.1% of men, including 8.2% with a PSA level of <10 ng/mL and 43% with a PSA level of >20 ng/mL. Metastases were identified in 6.4% with ISUP grade 2-3 and 21% with ISUP grade 4-5. Pre-biopsy mpMRI identified metastasis in 8.1% of T2 disease, increasing to 42.4% of T3b. Lymph node metastases were suspected in 107 men, with 47.7% outside the boundaries of an extended pelvic lymph node dissection. Skeletal metastases were identified in 4.7%. In men with intermediate-risk prostate cancer, metastases were identified in 5.2%, compared to 19.9% with high-risk disease. CONCLUSIONS: These results support the use of 68 Ga-PSMA PET/CT for primary staging of prostate cancer. Increasing PSA level, ISUP grade and radiological staging with mpMRI were all statistically significant prognostic factors for metastasis on both univariate and multivariate analysis.

PSMA-PET guided hook-wire localization of nodal metastases in prostate cancer: a targeted approach.

Prostate Specific Membrane Antigen Positron Emission Tomography/Computed Tomography (PSMA-PET/CT) has increased the sensitivity and specificity of imaging to identify metastatic prostate cancer in the group of patients with early biochemical recurrence when compared to conventional imaging. In patients who develop biochemical recurrence of prostate cancer following surgical resection, salvage lymph node dissection may reduce prostate specific antigen (PSA) levels and delay the time for commencement of systemic therapies. However, PLND may be an anatomically and technically difficult procedure, particularly with small metastatic diseases which can be problematic for intra-operative identification. We describe the technique using PSMA-PET imaging to pre-operatively localise areas of low-volume nodal metastatic disease with hookwire to allow targeted lymph node dissection with direct visualisation and palpation to ensure adequate clearance of involved nodes.

Reconsidering the role of pelvic lymph node dissection with radical prostatectomy for prostate cancer in an era of improving radiological staging techniques.

BACKGROUND: Performing an extended pelvic lymph node dissection (PLND) on all men with intermediate- and high-risk prostate cancer at the time of a radical prostatectomy (RP) remains controversial. The majority of patients PLND histology is benign, and the long-term cancer-free progression in men with positive lymph node metastasis is low. The objective is to investigate the probability of long-term biochemical freedom from recurrent disease (bNED) in men with lymph node metastasis identified at the time of radical prostatectomy (RP). SUBJECTS AND METHODS: A retrospective review of the pathology of 1184 pelvic lymph node dissections performed at the time of a radical prostatectomy by multiple surgeons referred to a single uro-pathology laboratory between 2008 and 2014 identified 61 men with node-positive prostate cancer. Of the men with positive nodes, 24 had a standard PLND and 37 an extended PLND (ePLND). bNED was defined as a post-operative serum PSA < 0.2 ng/ml. RESULTS: The median follow-up is 4 years (2-8). The median lymph node count was 7 (range 2-16) for PLND and 22 (range 6-46) for the ePLND. A single lymph node metastasis was identified in 56% of the 61 men. Only 10% of men with a positive lymph node metastasis remained free of biochemical recurrence of disease, and only 5% had undetectable serum PSA. There was no difference in bNED outcome between a PLND and ePLND. The number of men needed to be treated with a PLND at the time of RP (NNT) to result in an undetectable post-operative PSA at a median follow-up of 4 years is 395. CONCLUSIONS: In men with lymph node metastasis, the probability of long-term bNED is low and the NNT for cure is high. With emerging improved radiological imaging techniques increasing the detection of lymph node metastasis outside the extended lymph node dissection templates, more scientific investigation is required to evaluate which men will benefit from a PLND and which men can avoid an unnecessary PLND procedure.