Diverse PSMA expression in primary prostate cancer: reason for negative [68Ga]Ga-PSMA PET/CT scans? Immunohistochemical validation in 40 surgical specimens

The Current Landscape of Prostate-Specific Membrane Antigen (PSMA) Imaging Biomarkers for Aggressive Prostate Cancer

The review examines the vital role of prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) in the diagnosis, staging, and treatment of prostate cancer (PCa). It focuses on the superior diagnostic abilities of PSMA PET/CT for identifying both nodal and distant PCa, and its potential as a prognostic indicator for biochemical recurrence and overall survival. Additionally, we focused on the variability of PSMA's expression and its impact on personalised treatment, particularly the use of [177Lu] Lu-PSMA-617 radioligand therapy. This review emphasises the essential role of PSMA PET/CT in enhancing treatment approaches, improving patient outcomes, and reducing unnecessary interventions, positioning it as a key element in personalised PCa management.

Advances in radiology and pathology of prostate cancer: a review for the pathologist

Multiparametric magnetic resonance imaging (mpMRI) has improved systematic prostate biopsy procedures in the diagnosis of clinically significant prostate cancer (csPCa) by reducing the number of unnecessary biopsies; numerous level one evidence studies have confirmed the accuracy of MRI-targeted biopsy, but, still today, systematic prostate biopsy is recommended to reduce the 15-20% false negative rate of mpMRI. New advanced imaging has been proposed to detect suspicious lesions and perform targeted biopsies especially when mpMRI cannot be performed. Transrectal ultrasound (TRUS) modalities are emerging as methods with greater sensitivity and specificity for the detection of PCa compared to the traditional TRUS; these techniques include elastography and contrast-enhanced ultrasound, as well as improved B-mode and Doppler techniques. These modalities can be combined to define a novel ultrasound approach: multiparametric ultrasound (mpUS). More recently, micro-ultrasound (MicroUS) and prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) have demonstrated to be sensitive for the detection of primary prostatic lesions resulting highly correlated with the aggressiveness of the primary prostatic tumor. In parallel, artificial intelligence is advancing and is set out to deeply change both radiology and pathology. In this study we address the role, advantages and shortcomings of novel imaging techniques for Pca, and discuss future directions including the applications of artificial intelligence-based techniques to imaging as well as histology. The significance of these findings for the practicing pathologist is discussed.

Targeted Biopsy in Men High Risk for Prostate Cancer: 68Ga-PSMA PET/CT Versus mpMRI

INTRODUCTION/BACKGROUND

To evaluate the accuracy of 68Ga-PSMA PET/CT versus mpMRI targeted biopsy (TPBx) in the diagnosis of clinically significant prostate cancer (csPCa) in men high risk for PCa.

MATERIALS AND METHODS

From January 2021 to March 2023, 125 men with clinical parameters high risk for PCa were evaluated by mpMRI and 68Ga-PSMA PET/CT; median PSA was 32.5 ng/mL (range: 12-160 ng/mL) and 60/125 (48%) had abnormal digital rectal examination. The mpMRI lesions with PI-RADS scores ≥ 3 and/or 68Ga-PSMA areas characterized by a standardized uptake value (SUVmax) values ≥ 8 were submitted to TPBx (4 cores); in addition, all the patients underwent systematic transperineal prostate biopsy (18 cores) under sedation and antibiotic prophylaxis.

RESULTS

In 80 of 125 men (64%) a csPCa was found: 10 (12.5%) had a ISUP Grade Group 3 (GG), 45 (56.2%) a ISUP GG4 and 25 (31.2%) ISUP GG5. The median intraprostatic 68Ga-PSMA SUVmax was 42.3 (range:10.5-164) and 72 of 80 (90%) had a PI-RADS score ≥ 3. 68GaPSMA PET/CT showed the presence of metastases in 20 of 80 (25%) men: the median SUVmax in bone (15 cases) and nodes (40 cases) metastases was 55 and 47, respectively. Accuracy of 68Ga PSMA PET/CT (SUVmax cut-off ≥ 8) versus mpMRI PI-RADS score ≥ 3 in the diagnosis of csPCa was 92 versus 86.2%.

CONCLUSION

68GaPSMA PET/CT demonstrated a good diagnostic accuracy as a single procedure for the diagnosis and staging of high-risk PCa.

Heterogeneity of prostate-specific membrane antigen (PSMA) and PSMA-ligand uptake detection combining autoradiography and postoperative pathology in primary prostate cancer

BACKGROUND

Targeting prostate-specific membrane antigen (PSMA) has been highly successful for imaging and treatment of prostate cancer. However, heterogeneity in immunohistochemistry indicates limitations in the effect of imaging and radionuclide therapy of multifocal disease. 99mTc-PSMA-I&S is a γ-emitting probe, which can be used for intraoperative lesion detection and postsurgical autoradiography (ARG). We aimed to study its intraprostatic distribution and compared it with (immuno)-histopathology.

RESULTS

Seventeen patients who underwent RGS between 11/2018 and 01/2020 with a total of 4660 grids were included in the preliminary analysis. Marked intratumor and intra-patient heterogeneity of PSMA expression was detected, and PSMA negative foci were observed in all samples (100%). Heterogeneous intra-patient PSMA-ligand uptake was observed, and no significant correlation was present between the degree of heterogeneity of PSMA expression and PSMA-ligand uptake. Higher PSMA-ligand uptake was observed in GS ≥ 8 than GS < 8 (p < 0.001). The appearance of Gleason Pattern (GP) 4 was strongly associated with higher uptake (coefficient: 0.43, p < 0.001), while GP 5 also affected the uptake (coefficient: 0.07, p < 0.001).

CONCLUSION

PSMA expression and PSMA-ligand uptake show marked heterogeneity. Prostate carcinoma with GP 4 showed significantly higher uptake compared with non-neoplastic prostate tissue. Our analyses extend the scope of applications of radiolabeled PSMA-ligands to ARG for identifying high-grade disease and using its signal as a noninvasive biomarker in prostate cancer.

Evaluating the value of 18F-PSMA-1007 PET/CT in the detection and identification of prostate cancer using histopathology as the standard

BACKGROUND

Prostate-specific membrane antigen (PSMA) PET/CT is a highly regarded radionuclide imaging modality for prostate cancer (PCa). This study aimed to evaluate the diagnostic performance of 18F-PSMA-1007 PET/CT in detecting intraprostatic lesions of PCa using radical prostatectomy (RP) specimens as a reference standard and to establish an optimal maximum standardized uptake value (SUVmax) cutoff for distinguishing between PCa and non-PCa lesions.

METHODS

We retrospectively collected 117 patients who underwent 18F-PSMA-1007 PET/CT before RP. The uptake of the index tumor and contralateral non-PCa lesion was assessed. Histopathology of RP specimens was used as the gold standard. Kappa test was used to evaluate the consistency of preoperative PSMA PET/CT staging and postoperative pathological staging. Finally, an SUVmax cutoff value was identified by receiver operating characteristic (ROC) curve analysis to distinguish PCa lesions from non-PCa lesions. A prospective cohort including 76 patients was used to validate the results.

RESULTS

The detection rate of 18F-PSMA-1007 PET/CT for prostate cancer was 96.6% (113/117). 18F-PSMA-1007 had a sensitivity of 91.2% and a positive predictive value (PPV) of 89.8% for the identification of intraprostatic lesions. The consistency test (Kappa = 0.305) indicated poor agreement between the pathologic T-stage and PSMA PET/CT T-stage. Based on ROC curve analysis, the appropriate SUVmax to diagnose PCa lesions was 8.3 (sensitivity of 71.3% and specificity 96.8%) with an area under the curve (AUC) of 0.93 (P < 0.001). This SUVmax cutoff discriminated PCa lesions from non-PCa lesions with a sensitivity of 74.4%, a specificity of 95.8% in the prospective validation group.

CONCLUSIONS

18F-PSMA-1007 PET/CT demonstrated excellent performance in detecting PCa. An optimal SUVmax threshold (8.3) could be utilized to identify lesions of PCa by 18F-PSMA-1007 PET/CT.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT04521894, Registered: August 17, 2020.

Development of [177Lu]Lu-LNC1003 for radioligand therapy of prostate cancer with a moderate level of PSMA expression

PURPOSE

Evans blue as an albumin binder has been widely used to improve pharmacokinetics and enhance tumor uptake of radioligands, including prostate-specific membrane antigen (PSMA) targeting agents. The goal of this study is to develop an optimal Evans blue-modified radiotherapeutic agent that could maximize the absolute tumor uptake and tumor absorbed dose thus the therapeutic efficacy to allow treatment of tumors even with moderate level of PSMA expression.

METHODS

[177Lu]Lu-LNC1003 was synthesized based on PSMA-targeting agent and Evans blue. Binding affinity and PSMA targeting specificity were verified through cell uptake and competition binding assay in 22Rv1 tumor model that has moderate level of PSMA expression. SPECT/CT imaging and biodistribution studies in 22Rv1 tumor-bearing mice were performed to evaluate the preclinical pharmacokinetics. Radioligand therapy studies were conducted to systematically assess the therapeutic effect of [177Lu]Lu-LNC1003.

RESULTS

LNC1003 showed high binding affinity (IC50 = 10.77 nM) to PSMA in vitro, which was comparable with that of PSMA-617 (IC50 = 27.49 nM) and EB-PSMA-617 (IC50 = 7.91 nM). SPECT imaging of [177Lu]Lu-LNC1003 demonstrated significantly improved tumor uptake and retention as compared with [177Lu]Lu-EB-PSMA and [177Lu]Lu-PSMA-617, making it suitable for prostate cancer therapy. Biodistribution studies further confirmed the remarkably higher tumor uptake of [177Lu]Lu-LNC1003 (138.87 ± 26.53%ID/g) over [177Lu]Lu-EB-PSMA-617 (29.89 ± 8.86%ID/g) and [177Lu]Lu-PSMA-617 (4.28 ± 0.25%ID/g) at 24 h post-injection. Targeted radioligand therapy results showed noteworthy inhibition of 22Rv1 tumor growth after administration of a single dose of 18.5 MBq [177Lu]Lu-LNC1003. There was no obvious antitumor effect after [177Lu]Lu-PSMA-617 treatment under the same condition.

CONCLUSION

In this study, [177Lu]Lu-LNC1003 was successfully synthesized with high radiochemical purity and stability. High binding affinity and PSMA targeting specificity were identified in vitro and in vivo. With greatly enhanced tumor uptake and retention, [177Lu]Lu-LNC1003 has the potential to improve therapeutic efficacy using significantly lower dosages and less cycles of 177Lu that promises clinical translation to treat prostate cancer with various levels of PSMA expression.

The Impact of PSMA PET/CT on Modern Prostate Cancer Management and Decision Making-The Urological Perspective

Prostate-specific membrane antigen (PSMA) PET use in prostate cancer treatment has recently become a routinely used imaging modality by urologists. New, established data regarding its performance in different stages of prostate cancer, as well as gaining clinical knowledge with new tracers, drives the need for urologists and other clinicians to improve the utilization of this tool. While the use of PSMA PET/CT is more common in metastatic disease, in which it outperforms classical imaging modalities and drives treatment decisions and adjustments, recently, it gained ground in localized prostate cancer as well, especially in high-risk disease. Still, PSMA PET/CT might reveal lesions within the prostate or possibly locoregional or metastatic disease, not always representing true cancer when utilized in earlier stages of the disease, potentially adding diagnostic burden and changing treatment decisions. As urological treatment options advance toward focal treatments in localized organ-confined prostate cancer, recent reports suggest the utilization of PSMA PET/CT in treatment planning and follow-up and even when choosing active surveillance. This review aims to reveal the current perspective of urologists regarding its daily use.

Feasibility of 99mTc-MIP-1404 for SPECT/CT Imaging and Subsequent PSMA-Radioguided Surgery in Early Biochemically Recurrent Prostate Cancer: A Case Series of 9 Patients

This case series evaluated the feasibility of prostate-specific membrane antigen (PSMA)-radioguided surgery (RGS) with ^99mTc-MIP-1404 in recurrent prostate cancer. Methods: Nine patients with PSMA-positive lesions on PET/CT received ^99mTc-MIP-1404 (median, 747 MBq; interquartile range [IQR], 710-764 MBq) 17.2 h (IQR, 16.9-17.5 h) before SPECT/CT and 22.3 h (IQR, 20.8-24.0 h) before RGS. Results: Seventeen PSMA-positive lesions were detected on PET/CT (median short-axis diameter, 4 mm; IQR, 3-6 mm; median SUV_max, 8.9; IQR, 5.2-12.6). Nine of 17 (52.9%) were visible on SPECT/CT (median SUV_max, 13.8; IQR, 8.0-17.9). Except for 2 foci, all PET/CT-positive findings demonstrated intraoperative count rates above the background level (median count, 31; IQR, 17-89) and were lymph node metastases. Moreover, PSMA-RGS identified 2 additional metastases compared with PET/CT. Prostate-specific antigen values decreased after RGS in 6 of 9 patients (67%). Conclusion: PSMA-RGS with ^99mTc-MIP-1404 identified lymph node metastases in all patients, including 2 additional lesions compared with PET/CT.

Digital PET/CT with 18F-FACBC in early castration-resistant prostate cancer: our preliminary results

BACKGROUND

We assessed the role of digital PET/CT (dPET/CT) with ¹⁸F-FACBC in patients affected by castration-resistant prostate cancer with PSA levels ≤ 3 ng/mL (early CRPC), no lesions detectable at cross-sectional imaging (CIM) and bone scan (BS).

METHODS

Clinical data of patients submitted to ¹⁸F-FACBC dPET/CT were retrospectively reviewed. PET/CT results were analyzed: lesions' number, location, and, in case of positive lymph nodes, largest node's short axis (i.e. SA) were annotated. According to PET/CT's results, patients with ¹⁸F-FACBC-avid lesions were further stratified into 1) unifocal; 2) oligometastatic (≤ 5 lesions); 3) disseminated (> 6 lesions).

RESULTS

Twenty-four patients were enrolled. ¹⁸F-FACBC dPET/CT was positive in 21 out of 24 patients (87.5%). Thirteen patients (54.1%) showed recurrence in pelvic region, seven of whom with pelvic nodes' involvement, while eight cases (33.3%) presented ¹⁸F-FACBC-avid metastases to extra-pelvic nodes or bone. Average SA of PET-positive nodes resulted in 8.9 ± 3 mm. Patients were categorized as unifocal in four cases (26.6%), oligometastatic in 10 subjects (66.6%) and disseminated in 1 case (0.6%). PET/CT impacted on clinical management in 14 cases (58.3%).

CONCLUSIONS

¹⁸F-FACBC dPET/CT detected M1 status in 33.3% of early CRPC patients, significantly impacting on clinical management.