Immunohistochemical PSMA expression patterns of primary prostate cancer tissue are associated with the detection rate of biochemical recurrence with 68Ga-PSMA-11-PET

Immunohistochemistry analysis of PSMA expression at prostatic biopsy in high-risk prostate cancer: potential implications for PSMA-PET patient selection

Introduction

Prostate-specific membrane antigen (PSMA) is a transmembrane protein expressed by normal prostatic tissue. Therefore, molecular imaging targeting PSMA (PSMA-PET) has gained particular interest and diffusion for PCa staging and restaging. Several factors may affect PSMA-PET results, and many tools have been proposed to improve patient selection. Furthermore, PSMA expression is not homogeneous among different tissues and within the prostate itself. The aims of this study were to evaluate immunohistochemistry (IHC) features of prostate biopsy samples and to assess their correlation with whole-mount specimens and PSMA-PET parameters.

Methods

We included consecutive high-risk PCa patients who underwent PSMA-PET for staging proposal at our institution from January 2022 to December 2022. The PET parameters selected were SUVmax, total volume (TV), and total lesion activity (TL). Each patient underwent multiparametric MRI (mpMRI) and fusion-targeted prostate biopsy prior to surgery. IHC analyses were performed on the index lesion cores. IHC visual score (VS) (1, 2, 3) and visual pattern (VP) (membranous, cytoplasmic, and combined) and the percentage of PSMA-negative tumor areas (PSMA%neg) within biopsy cores were evaluated.

Results

Forty-three patients who underwent robotic radical prostatectomy after PSMA-PET were available for analyses. Concordance between VS and VP at biopsy and final pathology showed a Cohen's kappa coefficient of 0.39 and 0.38, respectively. Patients with PSMA%neg <20% had a higher concordance in VS and VP (Cohen's kappa 0.49 and 0.4, respectively). No difference emerged in terms of median PSMA-TV (p = 0.3) and PSMA-TL (p = 0.9) according to VS at biopsy, while median SUVmax was higher in patients with VS 3 (p = 0.04). Higher SUVmax was associated with membranous and combined VP expression (p = 0.008). No difference emerged between patients with PSMA%neg <20% or PSMA%neg >20% on biopsy cores in terms of SUVmax, PSMA-TL, and PSMA-TV (p = 0.5, p = 0.5, and p = 0.9 respectively).

Conclusions

We found a correlation between IHC VS and VP on targeted biopsy cores and SUVmax at PSMA-PET. However, the correlation between the IHC parameters of biopsy cores and final pathology was not as high as expected. Nevertheless, the presence of PSMA%neg <20% seems to have a better concordance in terms of visual score.

Multiparametric MRI and 18F-PSMA-1007 PET/CT for the Detection of Clinically Significant Prostate Cancer

Background Multiparametric MRI (mpMRI) is effective for detecting prostate cancer (PCa); however, there is a high rate of equivocal Prostate Imaging Reporting and Data System (PI-RADS) 3 lesions and false-positive findings. Purpose To investigate whether fluorine 18 (18F) prostate-specific membrane antigen (PSMA) 1007 PET/CT after mpMRI can help detect localized clinically significant PCa (csPCa), particularly for equivocal PI-RADS 3 lesions. Materials and Methods This prospective study included participants with elevated prostate-specific antigen (PSA) levels referred for prostate mpMRI between September 2020 and February 2022. 18F-PSMA-1007 PET/CT was performed within 30 days of mpMRI and before biopsy. PI-RADS category and level of suspicion (LOS) were assessed. PI-RADS 3 or higher lesions at mpMRI and/or LOS 3 or higher lesions at 18F-PSMA-1007 PET/CT underwent targeted biopsies. PI-RADS 2 or lower and LOS 2 or lower lesions were considered nonsuspicious and were monitored during a 1-year follow-up by means of PSA testing. Diagnostic accuracy was assessed, with histologic examination serving as the reference standard. International Society of Urological Pathology (ISUP) grade 2 or higher was considered csPCa. Results Seventy-five participants (median age, 67 years [range, 52-77 years]) were assessed, with PI-RADS 1 or 2, PI-RADS 3, and PI-RADS 4 or 5 groups each including 25 participants. A total of 102 lesions were identified, of which 80 were PI-RADS 3 or higher and/or LOS 3 or higher and therefore underwent targeted biopsy. The per-participant sensitivity for the detection of csPCa was 95% and 91% for mpMRI and 18F-PSMA-1007 PET/CT, respectively, with respective specificities of 45% and 62%. 18F-PSMA-1007 PET/CT was used to correctly differentiate 17 of 26 PI-RADS 3 lesions (65%), with a negative and positive predictive value of 93% and 27%, respectively, for ruling out or detecting csPCa. One additional significant and one insignificant PCa lesion (PI-RADS 1 or 2) were found at 18F-PSMA-1007 PET/CT that otherwise would have remained undetected. Two participants had ISUP 2 tumors without PSMA uptake that were missed at PET/CT. Conclusion 18F-PSMA-1007 PET/CT showed good sensitivity and moderate specificity for the detection of csPCa and ruled this out in 93% of participants with PI-RADS 3 lesions. Clinical trial registration no. NCT04487847 © RSNA, 2024 Supplemental material is available for this article. See also the editorial by Turkbey in this issue.

Molecular imaging reveals the heterogeneous progression of tumor cells and tumor stroma: a practice of FDG PET and FAPI PET in diagnosing PSMA-negative bone metastases of progressive prostate cancer

Tumors are often with complex and heterogeneous biological processes, such as glycometabolism and fibrosis, which are the main biochemical pathways that determine therapeutic effects. Specifically, this study aims to assess the diagnosing performance of 18F-FDG and 68Ga-FAPI-04 PET for different stages of progressive bone metastases with PSMA-negative pathology. Bone metastatic mouse model of prostate cancer was constructed via intra-bone injection of PSMA-negative prostate cancer PC3 cells. Cellular uptakes of 18F-FDG and 68Ga-FAPI-04 were separately performed on PC3, NIH-3T3 (FAP-positive) and a mixture. 68Ga-PSMA-11, 18F-FDG and 68Ga-FAPI-04 PET/CT imaging were performed at 2, 4 weeks after tumor cell transplantation. Furthermore, PSMA and FAP expression in bone metastases were assessed by immunohistochemistry, and then compared with the imageological findings. On the cellular level, the independent tracer uptake on the basis of glycometabolism and fibrosis was observed. For animal imaging, 68Ga-PSMA-11 imaging showed weak or absent tracer uptake in PSMA-negative bone metastatic lesions. In contrast, 68Ga-FAPI-04 PET of bone metastases had a higher uptake and tumor-to-muscle (T/M) ratio than 18F-FDG PET that was relative steady during the observation, but T/M ratio of fibrosis gradually decreased with increasing tumor growth, which ranged from 5.11 ± 1.26 at 2 weeks to 3.54 ± 0.23 at 4 weeks, revealing the delayed formation of tumor stroma in rapid proliferation. In addition, PET imaging results were corroborated by immunohistochemical assessment. In conclusion, molecular imaging approach revealed the heterogeneous progression of tumor cells and tumor stroma of bone metastasis of prostate cancer, and further confirming the necessity of multi-molecular imaging in cancer imaging.

Role of FDG PET/CT in Management of Patients with Prostate Cancer

Prostate cancer is the second most common cancer in men worldwide. [18F]FDG PET/CT imaging, a well-known and effective technique for detecting malignancies, has not been considered a useful tool for prostate cancer imaging by many because of its perceived low [18F]FDG uptake. Incidentally detected focal [18F]FDG uptake in the prostate is not uncommon, and typically benign. Imaging features that would increase concern for an underlying prostatic carcinoma, include focal uptake in the periphery near the gland margin without calcifications. [18F]FDG PET/CT imaging provides little value in the initial staging of prostate cancer, particularly in the era of prostate specific membrane antigen (PSMA) radiotracer. In cases of biochemical recurrence, the value of [18F]FDG PET/CT increases notably when Grade group 4 or 5 and elevated PSA levels are present. Active research is underway for theranostic approaches to prostate cancer, including [177Lu]Lu-PSMA therapy. Dual tracer staging using FDG and PSMA imaging significantly enhances the accuracy of disease site assessment. Specifically, the addition of [18F]FDG PET/CT imaging allows for the evaluation of discordant disease (PSMA negative/FDG positive). The maximal benefit from [177Lu]Lu-PSMA therapy relies on significant PSMA accumulation across all disease sites, and the identification of discordant disease suggests that these patients may derive less benefit from the treatment. The genuine value of [18F]FDG PET/CT imaging lies in advanced prostate cancer, PSMA-negative disease, as a prognostic biomarker, and the realm of new targeted theranostic agents.

Recurrent prostate cancer: combined role for MRI and PSMA-PET in 68Ga-PSMA-11 PET/MRI

OBJECTIVES

To investigate the specific strengths of MRI and PET components in 68Ga-PSMA-11 PET/MRI for staging of patients with biochemically recurrent prostate cancer (PCa).

METHODS

Patients with biochemical recurrence of PCa and contrast-enhanced whole-body 68Ga-PSMA-11 PET/MRI including a dedicated pelvic multiparametric MRI were included in this retrospective study. Imaging datasets of MRI and PET were evaluated separately regarding local PCa recurrence (Tr), pelvic lymph node metastases (N1), distant lymph node metastases (M1a), bone metastases (M1b), and soft tissue metastases (M1c) according to PROMISE version 1. Data evaluation was performed patient- and region-/lesion-based. Cox regression revealed a PSA of 1.69 ng/mL as a cut-off for subgroup analysis. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy were evaluated for each image component. Differences in staging accuracy were assessed using the Wilcoxon and McNemar test.

RESULTS

Altogether 102 patients (mean aged 68 ± 8 years, median PSA 1.33 ng/mL) were included. PCa was found in 70/102 (68%) patients. Accuracy of MRI in the detection of Tr, N1, M + , M1a, and M1b was 100%, 79%, 90%, 97%, and 95% for PSA < 1.69 ng/mL and 100%, 87%, 87%, 91%, and 96% for PSA > 1.69 ng/mL. Accuracy of 68Ga-PSMA-11 PET was 93%, 97%, 93%, 98%, and 100% for PSA < 1.69 ng/mL and 87%, 91%, 96%, 100%, and 96% for PSA > 1.69 ng/mL.

CONCLUSIONS

Combined assessment of 68Ga-PSMA-11 PET/MRI improves tumor localization in men with biochemical recurrence. The MRI detected local recurrence of PCa more often whereas 68 Ga-PSMA-11 PET detected lymph node metastases more often, especially for PSA < 1.69 ng/mL.

CLINICAL RELEVANCE STATEMENT

This study gives a scientific baseline to improve the understanding and reading of 68Ga-PSMA-11 PET/MRI imaging in patients with biochemically recurrent PCa by showing the specific strength of each imaging component.

KEY POINTS

• Combining the individual modality strengths of 68Ga-PSMA-11 PET/MRI improves tumor localization in men with biochemical recurrence of prostate cancer. • MRI component of 68 Ga-PSMA-11 PET/MRI shows its strength in detecting local recurrence of prostate cancer, especially at PSA < 1.69 ng/mL. • 68 Ga-PSMA-11 PET component shows its strength in detecting local and distant lymph node metastases, especially at PSA < 1.69 ng/mL.

PSMA-Expression Is Highly Associated with Histological Subtypes of Renal Cell Carcinoma: Potential Implications for Theranostic Approaches

In renal cell carcinoma (RCC), accurate imaging methods are required for treatment planning and response assessment to therapy. In addition, there is an urgent need for new therapeutic options, especially in metastatic RCC. One way to combine diagnostics and therapy in a so-called theranostic approach is the use of radioligands directed against surface antigens. For instance, radioligands against prostate-specific membrane antigen (PSMA) have already been successfully used for diagnosis and radionuclide therapy of metastatic prostate cancer. Recent studies have demonstrated that PSMA is expressed not only in prostate cancer but also in the neovasculature of several solid tumors, which has raised hopes to use PSMA-guided theranostic approaches in other tumor entities, too. However, data on PSMA expression in different histopathological subtypes of RCC are sparse. Because a better understanding of PSMA expression in RCC is critical to assess which patients would benefit most from theranostic approaches using PSMA-targeted ligands, we investigated the expression pattern of PSMA in different subtypes of RCC on protein level. Immunohistochemical staining for PSMA was performed on formalin-fixed, paraffin-embedded archival material of major different histological subtypes of RCC (clear cell RCC (ccRCC)), papillary RCC (pRCC) and chromophobe RCC (cpRCC). The extent and intensity of PSMA staining were scored semi-quantitatively and correlated with the histological RCC subtypes. Group comparisons were calculated with the Kruskal-Wallis test. In all cases, immunoreactivity was detected only in the tumor-associated vessels and not in tumor cells. Staining intensity was the strongest in ccRCC, followed by cpRCC and pRCC. ccRCC showed the most diffuse staining pattern, followed by cpRCC and pRCC. Our results provide a rationale for PSMA-targeted theranostic approaches in ccRCC and cpRCC.

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.

PSMA hybrid imaging in prostate cancer - current applications and perspectives

BACKGROUND

Prostate cancer (PCa) is the most common malignancy in men and the second most common tumor-associated cause of death in the male population in Germany. Prostate-specific membrane antigen (PSMA)-targeted hybrid imaging using positron emission tomography (PET) in combination with CT or MRI represents a comparably new method that gained increasing importance in the diagnostic process of PCa in recent years.

METHOD

Current applications of PSMA hybrid imaging were summarized according to the German and European guidelines on PCa. New developments were elaborated based on a literature review of PubMed conducted in 10/22.

RESULTS

PSMA-PET/CT demonstrated higher detection rates for metastases in high-risk PCa and recurrent PCa after primary therapy than established imaging methods (CT, MRI, and bone scan). Despite promising results from prospective trials in both scenarios and substantial influence on clinical decision making, data regarding the influence of PSMA-PET on PCa-specific and overall survival are still lacking. Hence, PSMA PET/CT is recommended with a "weak" strength rating in most situations. However, its importance in new treatment options like metastasis-directed therapy or PSMA-radioligand therapy expands the scope of PSMA-PET in the clinical routine.

CONCLUSION

PSMA-targeting hybrid imaging represents the most sensitive diagnostic test in several stages of PCa and allows the development of new treatment strategies. Prospective studies are needed to evaluate the influence of PSMA-PET on patient survival.

KEY POINTS

· PSMA-PET/CT is superior to conventional imaging in the primary staging of high-risk prostate cancer.. · PSMA hybrid imaging can detect metastases in patients with biochemical recurrence at low PSA values.. · Clinical decision making is frequently influenced by results of PSMA-PET/CT..

CITATION FORMAT

· Koehler D, Berliner C, Shenas F et al. PSMA hybrid imaging in prostate cancer - current applications and perspectives. Fortschr Röntgenstr 2023; 195: 1001 - 1008.

PET Imaging and Protein Expression of Prostate-Specific Membrane Antigen in Glioblastoma: A Multicenter Inventory Study

Upregulation of prostate-specific membrane antigen (PSMA) in neovasculature has been described in glioblastoma multiforme (GBM), whereas vasculature in nonaffected brain shows hardly any expression of PSMA. It is unclear whether PSMA-targeting tracer uptake on PET is based on PSMA-specific binding to neovasculature or aspecific uptake in tumor. Here, we quantified uptake of various PSMA-targeting tracers in GBM and correlated this with PSMA expression in tumor biopsy samples from the same patients. Methods: Fourteen patients diagnosed with de novo (n = 8) or recurrent (n = 6) GBM underwent a preoperative PET scan after injection of 1.5 MBq/kg [68Ga]Ga-PSMA-11 (n = 7), 200 MBq of [18F]DCFpyl (n = 3), or 200 MBq of [18F]PSMA-1007 (n = 4). Uptake in tumor and tumor-to-background ratios, with contralateral nonaffected brain as background, were determined. In a subset of patients, PSMA expression levels from different regions in the tumor tissue samples (n = 40), determined using immunohistochemistry (n = 35) or RNA sequencing (n = 13), were correlated with tracer uptake on PET. Results: Moderate to high (SUVmax, 1.3-20.0) heterogeneous uptake was found in all tumors irrespective of the tracer type used. Uptake in nonaffected brain was low, resulting in high tumor-to-background ratios (6.1-359.0) calculated by dividing SUVmax of tumor by SUVmax of background. Immunohistochemistry showed variable PSMA expression on endothelial cells of tumor microvasculature, as well as on dispersed individual cells (of unknown origin), and granular staining of the neuropil. No correlation was found between in vivo uptake and PSMA expression levels (for immunohistochemistry, r = -0.173, P = 0.320; for RNA, r = -0.033, P = 0.915). Conclusion: Our results indicate the potential use of various PSMA-targeting tracers in GBM. However, we found no correlation between PSMA expression levels on immunohistochemistry and uptake intensity on PET. Whether this may be explained by methodologic reasons, such as the inability to measure functionally active PSMA with immunohistochemistry, tracer pharmacokinetics, or the contribution of a disturbed blood-brain barrier to tracer retention, should still be investigated.

The Application of Radiolabeled Targeted Molecular Probes for the Diagnosis and Treatment of Prostate Cancer

Radiopharmaceuticals targeting prostate-specific membrane antigens (PSMA) are essential for the diagnosis, evaluation, and treatment of prostate cancer (PCa), particularly metastatic castration-resistant PCa, for which conventional treatment is ineffective. These molecular probes include [⁶⁸Ga]PSMA, [¹⁸F]PSMA, [Al¹⁸F]PSMA, [^99mTc]PSMA, and [⁸⁹Zr]PSMA, which are widely used for diagnosis, and [¹⁷⁷Lu]PSMA and [²²⁵Ac]PSMA, which are used for treatment. There are also new types of radiopharmaceuticals. Due to the differentiation and heterogeneity of tumor cells, a subtype of PCa with an extremely poor prognosis, referred to as neuroendocrine prostate cancer (NEPC), has emerged, and its diagnosis and treatment present great challenges. To improve the detection rate of NEPC and prolong patient survival, many researchers have investigated the use of relevant radiopharmaceuticals as targeted molecular probes for the detection and treatment of NEPC lesions, including DOTA-TOC and DOTA-TATE for somatostatin receptors, 4A06 for CUB domain-containing protein 1, and FDG. This review focused on the specific molecular targets and various radionuclides that have been developed for PCa in recent years, including those mentioned above and several others, and aimed to provide valuable up-to-date information and research ideas for future studies.

Novel Histopathological Biomarkers in Prostate Cancer: Implications and Perspectives

Prostate cancer (PCa) is the second most frequently diagnosed cancer in men. Despite the significant progress in cancer diagnosis and treatment over the last few years, the approach to disease detection and therapy still does not include histopathological biomarkers. The dissemination of PCa is strictly related to the creation of a premetastatic niche, which can be detected by altered levels of specific biomarkers. To date, the risk factors for biochemical recurrence include lymph node status, prostate-specific antigen (PSA), PSA density (PSAD), body mass index (BMI), pathological Gleason score, seminal vesicle invasion, extraprostatic extension, and intraductal carcinoma. In the future, biomarkers might represent another prognostic factor, as discussed in many studies. In this review, we focus on histopathological biomarkers (particularly CD169 macrophages, neuropilin-1, cofilin-1, interleukin-17, signal transducer and activator of transcription protein 3 (STAT3), LIM domain kinase 1 (LIMK1), CD15, AMACR, prostate-specific membrane antigen (PSMA), Appl1, Sortilin, Syndecan-1, and p63) and their potential application in decision making regarding the prognosis and treatment of PCa patients. We refer to studies that found a correlation between the levels of biomarkers and tumor characteristics as well as clinical outcomes. We also hypothesize about the potential use of histopathological markers as a target for novel immunotherapeutic drugs or targeted radionuclide therapy, which may be used as adjuvant therapy in the future.

PSMA PET/CT: joint EANM procedure guideline/SNMMI procedure standard for prostate cancer imaging 2.0

Here we aim to provide updated guidance and standards for the indication, acquisition, and interpretation of PSMA PET/CT for prostate cancer imaging. Procedures and characteristics are reported for a variety of available PSMA small radioligands. Different scenarios for the clinical use of PSMA-ligand PET/CT are discussed. This document provides clinicians and technicians with the best available evidence, to support the implementation of PSMA PET/CT imaging in research and routine practice.

18F-DCFPyL (PSMA) PET as a radiotherapy response assessment tool in metastatic prostate cancer

Background

Prostate Specific Membrane Antigen (PSMA) - positron emission tomography (PET) guides metastasis-directed radiotherapy (MDRT) in prostate cancer (PrCa). However, its value as a treatment response assessment tool after MDRT remains unclear. Importantly, there is limited understanding of the potential of radiotherapy (RT) to alter PSMA gene (folate hydrolase 1; FOLH1) expression.

Methodology

We reviewed a series of 11 men with oligo-metastatic PrCa (25 metastasis sites) treated with MDRT before re-staging with ¹⁸F-DCFPyL (PSMA) PET upon secondary recurrence. Acute effects of RT on PSMA protein and mRNA levels were examined with qPCR and immunoblotting in human wild-type androgen-sensitive (LNCap), castrate-resistant (22RV1) and castrate-resistant neuroendocrine (PC3 and DU145) PrCa cell lines. Xenograft tumors were analyzed with immunohistochemistry. Further, we examined PSMA expression in untreated and irradiated radio-resistant (RR) 22RV1 (22RV1-RR) and DU145 (DU145-RR) cells and xenografts selected for survival after high-dose RT.

Results

The majority of MDRT-treated lesions showed lack of PSMA-PET/CT avidity, suggesting treatment response even after low biological effective dose (BED) MDRT. We observed similar high degree of heterogeneity of PSMA expression in both human specimens and in xenograft tumors. PSMA was highly expressed in LNCap and 22RV1 cells and tumors but not in the neuroendocrine PC3 and DU145 models. Single fraction RT caused detectable reduction in PSMA protein but not in mRNA levels in LNCap cells and did not significantly alter PSMA protein or mRNA levels in tissue culture or xenografts of the other cell lines. However, radio-resistant 22RV1-RR cells and tumors demonstrated marked decrease of PSMA transcript and protein expression over their parental counterparts.

Conclusions

PSMA-PET may be a promising tool to assess RT response in oligo-metastatic PrCa. However, future systematic investigation of this concept should recognize the high degree of heterogeneity of PSMA expression within prostate tumors and the risk for loss of PSMA expression in tumor surviving curative courses of RT.

Gene's expression underpinning the divergent predictive value of [18F]F-fluorodeoxyglucose and prostate-specific membrane antigen positron emission tomography in primary prostate cancer: a bioinformatic and experimental study

BACKGROUND

Positron Emission Tomography (PET) imaging with Prostate-Specific Membrane Antigen (PSMA) and Fluorodeoxyglucose (FDG) represent promising biomarkers for risk-stratification of Prostate Cancer (PCa). We verified whether the expression of genes encoding for PSMA and enzymes regulating FDG cellular uptake are independent and additive prognosticators in PCa.

METHODS

mRNA expression of genes involved in glucose metabolism and PSMA regulation obtained from primary PCa specimens were retrieved from open-source databases and analyzed using an integrative bioinformatics approach. Machine Learning (ML) techniques were used to create predictive Progression-Free Survival (PFS) models. Cellular models of primary PCa with different aggressiveness were used to compare [18F]F-PSMA-1007 and [18F]F-FDG uptake kinetics in vitro. Confocal microscopy, immunofluorescence staining, and quantification analyses were performed to assess the intracellular and cellular membrane PSMA expression.

RESULTS

ML analyses identified a predictive functional network involving four glucose metabolism-related genes: ALDOB, CTH, PARP2, and SLC2A4. By contrast, FOLH1 expression (encoding for PSMA) did not provide any additive predictive value to the model. At a cellular level, the increase in proliferation rate and migratory potential by primary PCa cells was associated with enhanced FDG uptake and decreased PSMA retention (paralleled by the preferential intracellular localization).

CONCLUSIONS

The overexpression of a functional network involving four glucose metabolism-related genes identifies a higher risk of disease progression since the earliest phases of PCa, in agreement with the acknowledged prognostic value of FDG PET imaging. By contrast, the prognostic value of PSMA PET imaging is independent of the expression of its encoding gene FOLH1. Instead, it is influenced by the protein docking to the cell membrane, regulating its accessibility to tracer binding.

Using PSMA imaging for prognostication in localized and advanced prostate cancer

The use of prostate-specific membrane antigen (PSMA)-directed applications in modern prostate cancer management has evolved rapidly over the past few years, helping to establish new treatment pathways and provide further insights into prostate cancer biology. However, the prognostic implications of PSMA-PET have not been studied systematically, owing to rapid clinical implementation without long follow-up periods to determine intermediate-term and long-term oncological outcomes. Currently available data suggest that traditional prognostic factors and survival outcomes are associated with high PSMA expression (both according to immunohistochemistry and PET uptake) in men with localized and biochemically recurrent disease. Treatment with curative intent (primary and/or salvage) often fails when PSMA-positive metastases are present; however, the sensitivity of PSMA-PET in detecting all metastases is poor. Low PSMA-PET uptake in recurrent disease is a favourable prognostic factor; however, it can be associated with poor prognosis in conjunction with high ¹⁸F-fluorodeoxyglucose uptake in metastatic castration-resistant prostate cancer. Clinical trials embedding PSMA-PET for guiding management with reliable oncological outcomes are needed to support ongoing clinical use.

siAKR1C3@PPA complex nucleic acid nanoparticles inhibit castration-resistant prostate cancer in vitro

Introduction

AKR1C3, as a crucial androgenic enzyme, implicates the androgen biosynthesis and promoting prostate cancer cell growth in vitro. This study provides a new gene therapy strategy for targeting AKR1C3 to treat castration-resistant prostate cancer.

Methods

siAKR1C3@PPA is assembled from PEG3500, PAMAM, Aptamer-PSMA, and siRNA for AKR1C3. We analyzed the relationship between AKR1C3 expression and the survival rate of prostate cancer patients based on the GEPIA online database to perform disease-free survival, and found that AKR1C3 may be an important factor leading to poor prognosis in prostate cancer. Considering AKR1C3 as a therapeutic target for castration-resistant prostate cancer, we constructed a complex nucleic acid nanoparticle, siAKR1C3@PPA to investigate the inhibitory effect on castration-resistant prostate cancer.

Results

Aptamer-PSMA acts as a target to guide siAKR1C3@PPA into PSMA-positive prostate cancer cells and specifically down regulate AKR1C3. Cyclin D1 was decreased as a result of siAKR1C3@PPA treatment. Changes in Cyclin D1 were consistent with decreased expression of AKR1C3 in LNCaP-AKR1C3 cells and 22RV1 cells. Furthermore, in the LNCaP-AKR1C3 group, 1070 proteins were upregulated and 1015 proteins were downregulated compared to the LNCaP group according to quantitative 4D label-free proteomics. We found 42 proteins involved in cell cycle regulation. In a validated experiment, we demonstrated that PCNP and CINP were up-regulated, and TERF2 and TP53 were down-regulated by western blotting.

Conclusion

We concluded that siAKR1C3@PPA may arrest the cell cycle and affect cell proliferation.

Prostate-specific Membrane Antigen Biology in Lethal Prostate Cancer and its Therapeutic Implications

CONTEXT

Prostate-specific membrane antigen (PSMA) is a promising, novel theranostic target in advanced prostate cancer (PCa). Multiple PSMA-targeted therapies are currently in clinical development, with some agents showing impressive antitumour activity, although optimal patient selection and therapeutic resistance remain ongoing challenges.

OBJECTIVE

To review the biology of PSMA and recent advances in PSMA-targeted therapies in PCa, and to discuss potential strategies for patient selection and further therapeutic development.

EVIDENCE ACQUISITION

A comprehensive literature search was performed using PubMed and review of American Society of Clinical Oncology and European Society of Medical Oncology annual meeting abstracts up to April 2021.

EVIDENCE SYNTHESIS

PSMA is a largely extracellular protein that is frequently, but heterogeneously, expressed by PCa cells. PSMA expression is associated with disease progression, worse clinical outcomes and the presence of tumour defects in DNA damage repair (DDR). PSMA is also expressed by other cancer cell types and is implicated in glutamate and folate metabolism. It may confer a tumour survival advantage in conditions of cellular stress. PSMA regulation is complex, and recent studies have shed light on interactions with androgen receptor, PI3K/Akt, and DDR signalling. A phase 2 clinical trial has shown that 177Lu-PSMA-617 causes tumour shrinkage and delays disease progression in a significant subset of patients with metastatic castration-resistant PCa in comparison to second-line chemotherapy. Numerous novel PSMA-targeting immunotherapies, small molecules, and antibody therapies are currently in clinical development, including in earlier stages of PCa, with emerging evidence of antitumour activity. To date, the regulation and function of PSMA in PCa cells remain poorly understood.

CONCLUSIONS

There has been rapid recent progress in PSMA-targeted therapies for the management of advanced PCa. Dissection of PSMA biology will help to identify biomarkers for and resistance mechanisms to these therapies and facilitate further therapeutic development to improve PCa patient outcomes.

PATIENT SUMMARY

There have been major advances in the development of therapies targeting a molecule, PSMA, in PCa. Radioactive molecules targeting PSMA can cause tumour shrinkage and delay progression in some patients with lethal disease. Future studies are needed to determine which patients are most likely to respond, and how other treatments can be combined with therapies targeting PSMA so that more patients may benefit.

The Role of PSMA PET/CT in the Primary Diagnosis and Follow-Up of Prostate Cancer-A Practical Clinical Review

Simple Summary

The combination of positron emission tomography (PET)-diagnostics with ligands binding to the prostate-specific membrane antigen (PSMA) has been a diagnostic milestone in the situation of biochemical recurrence of prostate cancer and is gaining importance in primary diagnostics, providing a highly specific and sensitive diagnostic method in various clinical situations. However, the clinical application of this method requires a comprehensive knowledge of its advantages and disadvantages, potential pitfalls and influencing factors. This review aims to provide a practical clinical review of the currently available background data on PSMA PET/CT, as well as the clinical implications. Although a large amount of data already exist, a thorough analysis is complicated by study heterogeneity, showing the need for future systematic and prospective research.

Abstract

The importance of PSMA PET/CT in both primary diagnostics and prostate cancer recurrence has grown steadily since its introduction more than a decade ago. Over the past years, a vast amount of data have been published on the diagnostic accuracy and the impact of PSMA PET/CT on patient management. Nevertheless, a large heterogeneity between studies has made reaching a consensus difficult; this review aims to provide a comprehensive clinical review of the available scientific literature, covering the currently known data on physiological and pathological PSMA expression, influencing factors, the differences and pitfalls of various tracers, as well as the clinical implications in initial TNM-staging and in the situation of biochemical recurrence. This review has the objective of providing a practical clinical overview of the advantages and disadvantages of the examination in various clinical situations and the body of knowledge available, as well as open questions still requiring further research.

Predictors of Bone Metastases at 68Ga-PSMA-11 PET/CT in Hormone-Sensitive Prostate Cancer (HSPC) Patients with Early Biochemical Recurrence or Persistence

Prostate-specific-membrane-antigen/positron-emission-tomography (PSMA-PET) can accurately detect disease localizations in prostate cancer (PCa) patients with early biochemical recurrence/persistence (BCR/BCP), allowing for more personalized image-guided treatments in oligometastatic patients with major impact in the case of bone metastases (BM). Therefore, this study aimed to identify predictors of BM at PSMA-PET in early-BCR/BCP hormone-sensitive PCa (HSPC) patients, previously treated with radical intent (radiotherapy or radical prostatectomy ± salvage-radiotherapy (SRT)). A retrospective analysis was performed on 443 ⁶⁸Ga-PSMA-11-PET/CT scans. The cohort median PSA at PET-scan was 0.60 (IQR: 0.38–1.04) ng/mL. PSMA-PET detection rate was 42.0% (186/443), and distant lesions (M1a/b/c) were found in 17.6% (78/443) of cases. BM (M1b) were present in 9.9% (44/443) of cases, with 70.5% (31/44) showing oligometastatic spread (≤3 PSMA-positive lesions). In the multivariate binary logistic regression model (accuracy: 71.2%, Nagelkerke-R²: 13%), T stage ≥ 3a (OR: 2.52; 95% CI: 1.13–5.60; p = 0.024), clinical setting (previous SRT vs. first-time BCR OR: 2.90; 95% CI: 1.32–6.35; p = 0.008), and PSAdt (OR: 0.93; 95% CI: 0.88–0.99; p = 0.026) were proven to be significant predictors of bone metastases, with a 7% risk increment for each single-unit decrement of PSAdt. These predictors could be used to further refine the indication for PSMA-PET in early BCR/BCP HSPC patients, leading to higher detection rates of bone disease and more personalized treatments.

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

PURPOSE

The purpose of this study was to immunohistochemically validate the primary tumor PSMA expression in prostate cancer (PCa) patients imaged with [⁶⁸Ga]Ga-PSMA PET/CT prior to surgery, with special consideration of PET-negative cases.

METHODS

The study included 40 men with newly diagnosed treatment-naïve PCa imaged with [⁶⁸Ga]Ga-PSMA I&T PET/CT as part of the diagnostic work-up prior to radical prostatectomy. All primary tumors were routinely stained with H&E. In addition, immunohistochemical staining of PSMA was performed and the immunoreactive score (IRS) was computed as semiquantitative measure. Subsequently, imaging findings were correlated to histopathologic results.

RESULTS

Eighty-three percent (33/40) of patients presented focal uptake of [⁶⁸Ga]Ga-PSMA I&T in the primary tumor in at least one prostate lobe. Among PSMA-PET positive patients, one-third had lymph node metastases (LNM) detected by post-operative histopathology, while in PET negative patients, only 1 out of 7 presented with regional LN involvement; PSMA-avid distant lesions, predominantly in bones, were observed in 15% and 0% of patients, respectively. The median IRS classification of PSMA expression in tumor tissue was 2 (range, 1-3) both in PSMA-PET positive and negative prostate lobes, with significantly different interquartile range: 2-3 vs. 2-2, respectively (p = 0.03). The median volume of PSMA-PET positive tumors was 5.4 mL (0.2-32.9) as compared to 1.6 mL (0.3-18.3) of PET-negative tumors (p < 0.001). There was a significant but weak correlation between SUV_max and percentage of PSMA-positive tumor cells (r = 0.46, p < 0.001). A total of 35/44 (~80%) lobes were positive in PSMA-PET imaging, when a cut-off percentage of PSMA-positive cells was ≥ 90%, while 19/36 (~53%) lobes with < 90% PSMA-positive cells were PSMA-PET negative.

CONCLUSION

Positive [⁶⁸Ga]Ga-PSMA I&T PET/CT scan of primary tumor of PCa results from a combination of factors, such as homogeneity and intensity of PSMA expression, tumor volume and grade, with a cutoff value of ≥ 90% PSMA-positive cells strongly determining PET-positivity. Focal accumulation of [⁶⁸Ga]Ga-PSMA in the primary tumor may correlate positively with aggressiveness of prostate cancer, harboring higher risk of regional LN involvement and distant metastatic spread.

Immunohistochemical Expression Pattern of Theragnostic Targets SSTR2 and PSMA in Endolymphatic Sac Tumors: A Single Institution Case Series

BACKGROUND

Endolymphatic sac tumors are rare neoplasia characterized by slow growth. However, their clinical impact should not be underestimated, considering their potential for local aggressive behavior and strong association with von Hippel-Lindau syndrome. Therefore, early detection with emerging theragnostic examinations such as ⁶⁸Ga-DOTATATE-PET/CT might improve patient management and reduce morbidity.

METHODS

We report the clinicopathological features of seven endolymphatic sac tumors. In this cohort, we performed immunohistochemical analysis of somatostatin receptor 2A (SSTR2A) and prostate specific membrane antigen (PSMA) protein expression patterns; two targets providing rationale for novel imaging modalities such as PSMA- or SSTR-targeted PET.

RESULTS

The tumor cells of all cases were negative for prostate specific membrane antigen and somatostatin receptor 2A, however immunolabeling was consistently detected in intratumoral endothelial cells of endolymphatic sac tumors for PSMA (7/7 cases, 100%), and for SSTR2A (5/7 cases, 71%).

CONCLUSIONS

Our results show a high rate of PSMA and SSTR2A expression in the tumor vasculature of endolymphatic sac tumors. PSMA and SSTR2A can be targeted with appropriate radioligands for diagnostic and therapeutic purposes. This finding provides a rationale for prospective clinical studies to test this approach as a sensitive screening tool for patients with suspected endolymphatic sac tumors including an improved management of von Hippel-Lindau syndrome.

Infiltrative growth pattern of prostate cancer is associated with lower uptake on PSMA PET and reduced diffusion restriction on mpMRI

Purpose

Recently, a significant association was shown between novel growth patterns on histopathology of prostate cancer (PCa) and prostate-specific membrane antigen (PSMA) uptake on [⁶⁸Ga]PSMA-PET. It is the aim of this study to evaluate the association between these growth patterns and ADC (mm²/1000 s) values in comparison to [⁶⁸Ga]PSMA uptake on PET/MRI.

Methods

We retrospectively evaluated patients who underwent [⁶⁸Ga]PSMA PET/MRI for staging or biopsy guidance, followed by radical prostatectomy at our institution between 07/2016 and 01/2020. The dominant lesion per patient was selected based on histopathology and correlated to PET/MRI in a multidisciplinary meeting, and quantified using SUV_max for PSMA uptake and ADC_mean for diffusion restriction. PCa growth pattern was classified as expansive (EXP) or infiltrative (INF) according to its properties of forming a tumoral mass or infiltrating diffusely between benign glands by two independent pathologists. Furthermore, the corresponding WHO2016 ISUP tumor grade was evaluated. The t test was used to compare means, Pearson’s test for categorical correlation, Cohen’s kappa test for interrater agreement, and ROC curve to determine the best cutoff.

Results

Sixty-two patients were included (mean PSA 11.7 ± 12.5). The interrater agreement between both pathologists was almost perfect with κ = 0.81. While 25 lesions had an EXP-growth with an ADC_mean of 0.777 ± 0.109, 37 showed an INF-growth with a significantly higher ADC_mean of 1.079 ± 0.262 (p < 0.001). We also observed a significant difference regarding PSMA SUV_max for the EXP-growth (19.2 ± 10.9) versus the INF-growth (9.4 ± 6.2, p < 0.001). Within the lesions encompassing the EXP- or the INF-growth, no significant correlation between the ISUP groups and ADC_mean could be observed (p = 0.982 and p = 0.861, respectively).

Conclusion

PCa with INF-growth showed significantly lower SUV_max and higher ADC_mean values compared to PCa with EXP-growth. Within the growth groups, ADC_mean values were independent from ISUP grading.

Supplementary information

The online version contains supplementary material available at 10.1007/s00259-022-05787-9.

Event-free survival after 68 Ga-PSMA-11 PET/CT in recurrent hormone-sensitive prostate cancer (HSPC) patients eligible for salvage therapy

Background/aim

Prostate-specific-membrane-antigen/positron emission tomography (PSMA-PET) detects with high accuracy disease-recurrence, leading to changes in the management of biochemically-recurrent (BCR) prostate cancer (PCa). However, data regarding the oncological outcomes of patients who performed PSMA-PET are needed. The aim of this study was to evaluate the incidence of clinically relevant events during follow-up in patients who performed PSMA-PET for BCR after radical treatment.

Materials and methods

This analysis included consecutive, hormone-sensitive, hormone-free, recurrent PCa patients (HSPC) enrolled through a prospective study. All patients were eligible for salvage therapy, having at least 24 months of follow-up after PSMA-PET. The primary endpoint was the Event-Free Survival (EFS), defined as the time between the PSMA-PET and the date of event/last follow-up. The Kaplan–Meier method was used to estimate the EFS curves. EFS was also investigated by Cox proportional hazards regression. Events were defined as death, radiological progression, or PSA recurrence after therapy.

Results

One-hundred and seventy-six (n = 176) patients were analyzed (median PSA 0.62 [IQR: 0.43–1.00] ng/mL; median follow-up of 35.4 [IQR: 26.5–40.3] months). The EFS was 78.8% at 1 year, 65.2% (2 years), and 52.2% (3 years). Patients experiencing events during study follow-up had a significantly higher median PSA (0.81 [IQR: 0.53–1.28] vs 0.51 [IQR: 0.36–0.80] ng/mL) and a lower PSA doubling time (PSAdt) (5.4 [IQR: 3.7–11.6] vs 12.7 [IQR: 6.6–24.3] months) (p < 0.001) compared to event-free patients. The Kaplan–Meier curves showed that PSA > 0.5 ng/mL, PSAdt ≤ 6 months, and a positive PSMA-PET result were associated with a higher event rate (p < 0.01). No significant differences of event rates were observed in patients who received changes in therapy management after PSMA-PET vs. patients who did not receive therapy changes. Finally, PSA > 0.5 ng/mL and PSAdt ≤ 6 months were statistically significant event-predictors in multivariate model (p < 0.001).

Conclusion

Low PSA and long PSAdt were significant predictors of longer EFS. A lower incidence of events was observed in patients having negative PSMA-PET, since longer EFS was significantly more probable in case of a negative scan.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-022-05741-9.

Identification of the Optimal Cut-Off Value of PSA for Assessing Severity of Disease in [68Ga]Ga-PSMA-11 PET/CT Study in Prostate Cancer Patients after Radical Prostatectomy

Objective: The objective of this study was to identify the optimal cut-off value of prostate specific antigen (PSA) to assess the extent of the disease in [68Ga]Ga-PSMA-11 PET/CT study in patients after radical prostatectomy. Materials and Methods: Retrospective analysis was performed on a group of 215 patients who underwent a [68Ga]Ga-PSMA-11 PET/CT examination because of suspected recurrence after radical prostatectomy. Patients were divided into four groups: 1, no active lesions suggesting recurrence (n = 92); 2, suspected isolated local recurrence (n = 19); 3, oligometastatic disease (n = 82); and 4, polymetastatic disease (n = 22). Results: In group 1, the mean PSA level was 0.962 ng/mL (median: 0.376; min: 0.004; max: 25 ng/mL); in group 2, it was 4.970 ng/mL (median 1.320; min: 0.003; max: 40.350 ng/mL); in group 3, it was 2.802 ng/mL (median: 1.270; min: 0.020; max: 59.670 ng/mL); and in group 4, it was 4.997 ng/mL (median: 3.795; min: 0.007; max 21.110 ng/mL). Statistically significant differences were shown in PSA levels when comparing groups 1 and 2 (p = 0.0025) and groups 3 and 4 (p = 0.0474). The PSA cut-off point for discriminating groups 1 and 2 was 0.831 (sensitivity: 0.684; specificity: 0.772; area under the curve (AUC): 0.775), and for groups 3 and 4, it was 2.51 (sensitivity: 0.682; specificity: 0.780; AUC: 0.720). Conclusions: Our preliminary data suggested that the PSA level has an essential influence on determining the extent of disease in a [68Ga]Ga-PSMA-11 PET/CT study in patients after radical prostatectomy. Identification of the optimal cut-off values for the oligo- and polymetastatic diseases might be helpful in stratifying these patients.

PSMA PET in Imaging Prostate Cancer

After prostate malignancy diagnosis, precise determination of disease extent are fundamental steps for tailored made therapy. The earlier the diagnosis of the burden of the disease, the longer the survival in many cases. National and international guidelines are based on “classic” imaging technics combining radiological and nuclear medicine scans like CT, MRI and bone scintigraphy (BS). The most recent nuclear medicine development is the prostate specific membrane antigen (PSMA) PET and is emerging as the most promising tool of medical imaging, gaining ground every day. Nevertheless, the different onset among multiple studies fails to establish a worldwide admission and incorporation of this technique in guidelines and its position in workaday medical algorithms. It seems that the medical community agrees not to utilize PSMA PET for low-risk patients; intense debate and research is ongoing for its utility in intermediate risk patients. Contrariwise, in high-risk patients PSMA PET is confirmed outperforming CT and BS combined. Additionally, irrespectively to their castration status, patients with biochemical failure should be referred for PSMA PET. Even though PSMA PET reveals more extended disease than expected or exonerates equivalent lesions, thus impacting treatment optimization. Studies being in progress and future trials with clarify whether PSMA PET will be the new gold standard technic for specific groups of patients.

A glance at the emerging diagnostic biomarkers in the most prevalent genitourinary cancers

Genitourinary cancers comprise of a heterogenous group of cancers of which renal cell carcinoma, urothelial bladder carcinoma, and prostate adenocarcinoma are the most commonly encountered subtypes. A lot of research is ongoing using various strategies for exploration of novel biomarkers for genitourinary cancers. These biomarkers would not reduce the need for invasive diagnostic techniques but also could be used for early and accurate diagnosis to improve the clinical management required for the disease. Moreover, selecting the appropriate treatment regimen for the responsive patients based on these biomarkers would reduce the treatment toxicity as well as cost. Biomarkers identified using various advanced techniques like next generation sequencing and proteomics, which have been classified as immunological biomarkers, tissue-specific biomarkers and liquid biomarkers. Immunological biomarkers include markers of immunological pathways such as CTLA4, PD-1/PDl-1, tissue biomarkers include tissue specific molecules such as PSA antigen and liquid biomarkers include biomarkers detectable in urine, circulating cells etc.

The purpose of this review is to provide a brief introduction to the most prevalent genitourinary malignancies, including bladder, kidney, and prostate cancers along with a major focus on the novel diagnostic biomarkers and the importance of targeting them prior to genitourinary cancers treatment. Understanding these biomarkers and their potential in diagnosis of genitourinary cancer would not help in early and accurate diagnosis as mentioned above but may also lead towards a personalized approach for better diagnosis, prognosis and specified treatment approach for an individual.

The Value of Multimodality PET/CT Imaging in Detecting Prostate Cancer Biochemical Recurrence

Prostate cancer (PCa) induced death is the predominant cause of cancer-related death among men in 48 countries. After radical treatment, biochemical recurrence has become an important factor for prognosis. The early detection and diagnosis of recurrent lesions are very helpful in guiding treatment and improving the prognosis. PET/CT is a promising method for early detection of lesions in patients with biochemical recurrence of prostate cancer. This article reviews the progress of the research on PET/CT in the PCa biochemical recurrence and aims to introduce new technologies and provide more direction for future research.

Radiation Dosimetry in 177Lu-PSMA-617 Therapy

Radionuclide therapy using the small molecule PSMA bound to the beta-emitting radionuclide, Lutetium-177 (¹⁷⁷Lu-PSMA) has demonstrated efficacy and survival benefit castrate resistant metastatic disease and represents a novel new line of therapy. Whilst dosimetry was critical for early development, it was not incorporated into either the TheraP or VISION randomized studies, highlighting the difficulty of adopting dosimetry in routine clinical practice. Accumulated clinical experience has also shown that the common (and generally low grade) toxicities such as nausea, xerostomia, and cytopenias are not readily predicted on the basis of dosimetry estimates. The majority of dosimetry and clinical literature deals with the radiopharmaceutical ¹⁷⁷Lu-PSMA-617 which displays relatively consistent patterns of retention among normal tissues and high specificity for metastatic prostate cancer phenotypes. Population dosimetry incorporating estimates to the kidneys, salivary glands, and bone marrow have been widely reported the typical range of doses is becoming well established. There is growing interest on tumor dosimetry in ¹⁷⁷Lu-PSMA-617 therapy as an overall modest side-effect profile from primary organ retention has been observed. A focus away from normal organ dosimetry to whole body tumor dosimetry may enable early prediction of treatment failure. Given the safety of ¹⁷⁷Lu-PSMA there is also potential to escalate administered radioactivity to further improve outcomes. Importantly, the variability of uptake between individuals, both to tumor and normal organs, has also been highlighted which provides some rationale for the utility of personalized radiation analysis to optimize treatment based on potential toxicity thresholds or tumor control. Methods to perform dosimetry using serial post treatment imaging may incorporate planar, 3D SPECT, or hybrid datasets. Reliable measurements may be obtained through either method, however, continued developments in computational analysis are better suited to fully 3D imaging; particularly in conjunction with volumetric CT to assist with alignment and contouring. Dose analysis over sequential treatment cycles is vital to understand the radiobiology of these treatments which is unique compared to external beam therapy due to dose rate, fractionation scheme, and potential for intratumoral nonuniformity.

Digital PET and detection of recurrent prostate cancer: what have we gained, and what is still missing?

Defined by the TIME magazine 'medical invention of the year 2000,' positron emission computed tomography (PET/CT) has experienced impressive improvements in technology and clinical applications over time. In recent years, silicon photomultipliers (SiPMs) detectors, characterized by excellent intrinsic time resolution and high photon-detection efficiency, have been introduced as an alternative to the classic photomultiplier tubes (PMTs), thus moving the field of PET technology forward and leading to the so-called digital PET/CT (dPET/CT). On the other side, the radiopharmaceutical ⁶⁸Ga-PSMA-11, approved by the Food and Drug Administration in December 2020, proved to strongly impact prostate cancer (PCa) diagnosis and management. In the study under evaluation, Alberts et al. retrospectively compared the performance of dPET/CT and PMTs-based PET/CT, namely analogue PET/CT (aPET/CT), in two cohorts, each one including 65 patients undergoing PET/CT with ⁶⁸Ga-PSMA-11 for suspected recurrent PCa. The authors found that dPET/CT presented a higher detection rate of pathological lesions with respect to aPET/CT. Of note, dPET/CT's higher sensitivity results are associated with an increased true-positive rate and high inter-reader agreement. This report underscores how innovative PET/CT instrumentation, by utilizing novel radiopharmaceuticals targeting specific metabolic/molecular signatures expressed by PCa, may represent a successful weapon in uro-oncology.

What's behind 68Ga-PSMA-11 uptake in primary prostate cancer PET? Investigation of histopathological parameters and immunohistochemical PSMA expression patterns

Purpose

Prostate-specific membrane antigen (PSMA-) PET has become a promising tool in staging and restaging of prostate carcinoma (PCa). However, specific primary tumour features might impact accuracy of PSMA-PET for PCa detection. We investigated histopathological parameters and immunohistochemical PSMA expression patterns on radical prostatectomy (RPE) specimens and correlated them to the corresponding ⁶⁸Ga-PSMA-11-PET examinations.

Methods

RPE specimens of 62 patients with preoperative ⁶⁸Ga-PSMA-11-PET between 2016 and 2018 were analysed. WHO/ISUP grade groups, growth pattern (expansive vs. infiltrative), tumour area and diameter as well as immunohistochemical PSMA heterogeneity, intensity and negative tumour area (PSMA_%neg) were correlated with spatially corresponding SUV_max on ⁶⁸Ga-PSMA-11-PET in a multidisciplinary analysis.

Results

All tumours showed medium to strong membranous (2–3 +) and weak to strong cytoplasmic (1–3 +) PSMA expression. Heterogeneously expressed PSMA was found in 38 cases (61%). Twenty-five cases (40%) showed at least 5% and up to 80% PSMA_%neg. PSMA_%neg, infiltrative growth pattern, smaller tumour area and diameter and WHO/ISUP grade group 2 significantly correlated with lower SUV_max values. A ROC curve analysis revealed 20% PSMA_%neg as an optimal cutoff with the highest sensitivity and specificity (89% and 86%, AUC 0.923) for a negative PSMA-PET scan. A multiple logistic regression model revealed tumoural PSMA_%neg (p < 0.01, OR = 9.629) and growth pattern (p = 0.0497, OR = 306.537) as significant predictors for a negative PSMA-PET scan.

Conclusions

We describe PSMA_%neg, infiltrative growth pattern, smaller tumour size and WHO/ISUP grade group 2 as parameters associated with a lower ⁶⁸Ga-PSMA-11 uptake in prostate cancer. These findings can serve as fundament for future biopsy-based biomarker development to enable an individualized, tumour-adapted imaging approach.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-021-05501-1.

Radionuclide Therapy in Prostate Cancer: from standalone to combination PSMA theranostics

Despite significant advances in prostate cancer therapeutic development over the last two decades, metastatic prostate cancer remains a lethal disease. Prostate-specific membrane antigen (PSMA), which is markedly overexpressed by prostate cancer cells, including at metastatic sites, but have low normal tissue expression, has emerged as an important theranostic target for these diseases. Both beta-emitting and alpha-emitting PSMA-targeted radionuclide therapy (RNT) are in clinical development. Several of these agents have already shown promising activity, however, a significant subset of patients have primary resistant disease and secondary resistance invariably occurs. Further, the effect of these therapies on healthy organs limit their therapeutic window. Elucidating the biology of PSMA as well as characterising the pharmacokinetic and pharmacodynamic properties of PSMA-targeted RNT will facilitate therapeutic approaches aimed at improving efficacy and safety. In this review, we provide an overview of existing PSMA-targeting RNT and an update on novel combinatorial approaches.

Translational Development of a Zr-89-Labeled Inhibitor of Prostate-specific Membrane Antigen for PET Imaging in Prostate Cancer

Purpose

We present here a Zr-89-labeled inhibitor of prostate-specific membrane antigen (PSMA) as a complement to the already established F-18- or Ga-68-ligands.

Procedures

The precursor PSMA-DFO (ABX) was used for Zr-89-labeling. This is not an antibody, but a peptide analogue of the precursor for the production of [¹⁷⁷Lu]Lu-PSMA-617. The ligand [⁸⁹Zr]Zr-PSMA-DFO was compared with [⁶⁸Ga]Ga-PSMA-11 and [¹⁸F]F-JK-PSMA-7 in vitro by determination of the K_d value, cellular uptake, internalization in LNCaP cells, biodistribution studies with LNCaP prostate tumor xenografts in mice, and in vivo by small-animal PET imaging in LNCaP tumor mouse models. A first-in-human PET was performed with [⁸⁹Zr]Zr-PSMA-DFO on a patient presenting with a biochemical recurrence after brachytherapy and an ambiguous intraprostatic finding with [¹⁸F]F-JK-PSMA-7 but histologically benign cells in a prostate biopsy 7 months previously.

Results

[⁸⁹Zr]Zr-PSMA-DFO was prepared with a radiochemical purity ≥ 99.9% and a very high in vitro stability for up to 7 days at 37 °C. All radiotracers showed similar specific cellular binding and internalization, in vitro and comparable tumor uptake in biodistribution experiments during the first 5 h. The [⁸⁹Zr]Zr-PSMA-DFO achieved significantly higher tumor/background ratios in LNCaP tumor xenografts (tumor/blood: 309 ± 89, tumor/muscle: 450 ± 38) after 24 h than [⁶⁸Ga]Ga-PSMA-11 (tumor/blood: 112 ± 57, tumor/muscle: 58 ± 36) or [¹⁸F]F-JK-PSMA-7 (tumor/blood: 175 ± 30, tumor/muscle: 114 ± 14) after 4 h (p < 0.01). Small-animal PET imaging demonstrated in vivo that tumor visualization with [⁸⁹Zr]Zr-PSMA-DFO is comparable to [⁶⁸Ga]Ga-PSMA-11 or [¹⁸F]F-JK-PSMA-7 at early time points (1 h p.i.) and that PET scans up to 48 h p.i. clearly visualized the tumor at late time points. A late [⁸⁹Zr]Zr-PSMA-DFO PET scan on a patient with biochemical recurrence (BCR) had demonstrated intensive tracer accumulation in the right (SUV_max 13.25, 48 h p.i.) and in the left prostate lobe (SUV max 9.47), a repeat biopsy revealed cancer cells on both sides.

Conclusion

[⁸⁹Zr]Zr-PSMA-DFO is a promising PSMA PET tracer for detection of tumor areas with lower PSMA expression and thus warrants further clinical evaluation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11307-021-01632-x.

An 89Zr-labeled PSMA tracer for PET/CT imaging of prostate cancer patients

The short half-life of existing prostate-specific membrane antigen (PSMA) tracers limits their time for internalization into tumor cells after injection, which is an essential prerequisite for robust detection of tumor lesions with low PSMA expression on PET/CT scans. Due to its longer half-life, the ⁸⁹Zr-labeled ligand ⁸⁹Zr-PSMA-Df allows acquisition of PET scans up to 6 days after injection, thereby overcoming the above limitation. We investigated whether ⁸⁹Zr-PSMA-Df allowed more sensitive detection of weak PSMA-positive prostate cancer lesions. Methods: We selected 14 prostate cancer patients with biochemical recurrence who exhibited no PSMA-positive lesions on a PET scan acquired with existing PSMA tracers (⁶⁸Ga-PSMA-11, ¹⁸F-JK-PSMA-7). Within 5 weeks after the negative scan, we performed a second PSMA-PET scan using ⁸⁹Zr-PSMA-Df (117±16 MBq, PET acquisition within 6 days of injection). Results: ⁸⁹Zr-PSMA-Df detected 15 PSMA-positive lesions in 8/14 patients, who had a PET-negative reading of their initial PET scans with existing tracers. In these 8 patients, the new scans revealed localized recurrence of disease (3/8), metastases in lymph nodes (3/8), or lesions at distant sites (2/8). Based on these results, patients received lesion-targeted radiotherapies (5/8), androgen deprivation therapies (2/8), or no therapy (1/8). The plausibility of 14/15 lesions was supported by histology, clinical follow-up after radiotherapy or subsequent imaging. Furthermore, comparison of the 15 ⁸⁹Zr-PSMA-Df-positive lesions with their correlates on the original PET scan revealed that established tracers exhibited mild accumulation in 7/15 lesions but contrast-to-noise ratios (CNR) were too low for robust detection of these lesions (CNR 2.4±3.7 for established tracers vs. 10.2±8.5 for ⁸⁹Zr-PSMA-Df, P = 0.0014). The SUV_max of the 15 ⁸⁹Zr-PSMA-Df-positive lesions (11.5±5.8) was significantly higher than the SUV_max on the original PET scans (4.7±2.8, P = 0.0001). Kidneys were the most exposed organ with doses of 3.3±0.7 mGy/MBq. The effective dose was 0.15±0.04 mSv/MBq. Conclusion: In patients with weak PSMA expression, a longer period of time might be needed for ligand internalization than that offered by existing PSMA tracers to make lesions visible on PET/CT scans. Hence, ⁸⁹Zr-PSMA-Df might be of significant benefit to patients in whom the search for weak PSMA-positive lesions is challenging. Radiation exposure should be weighed against the potential benefit of metastasis-directed therapy or salvage radiotherapy, which we initiated in 36% (5/14) of our patients based on their ⁸⁹Zr-PSMA-Df PET scans.

Establishment and prospective validation of an SUVmax cutoff value to discriminate clinically significant prostate cancer from benign prostate diseases in patients with suspected prostate cancer by 68Ga-PSMA PET/CT: a real-world study

Background and Aims: The aims of this study were to establish a maximum standardized uptake value (SUV_max) cutoff to discriminate clinically significant prostate cancer (csPCa) from benign prostate disease (BPD) by ⁶⁸Ga-labeled prostate-specific membrane antigen (⁶⁸Ga-PSMA-11) positron emission tomography/computed tomography (PET/CT) in patients with suspected prostate cancer (PCa), and to perform a prospective real-world validation of this cutoff value.

Methods: The study included a training cohort to identify an SUV_max cutoff value and a prospective real-world cohort to validate it. A retrospective analysis assessed 135 patients with suspected PCa in a large tertiary care hospital in China who underwent ⁶⁸Ga-PSMA-11 PET/CT. All patients were suspected of having PCa based on symptoms, digital rectal examination (DRE), total prostate-specific antigen (tPSA) level, and multiparameter magnetic resonance imaging (mpMRI). The ⁶⁸Ga-PSMA PET/CT results were evaluated using histopathological results from transrectal ultrasound-guided 12-core biopsy with necessary targeted biopsy as references. Patients with Gleason scores (GS) ≥7 from the biopsy results were diagnosed with csPCa, and patients with negative biopsy and follow-up results were diagnosed with BPD. Receiver operating characteristic (ROC) curve analysis was used to identify the optimal SUV_max cutoff value. The cutoff value was prospectively validated in 58 patients with suspected PCa. The diagnostic benefits of the cutoff value for clinical decision making were also evaluated.

Results: According to ROC curve analysis, the most appropriate SUV_max cutoff value for discriminating csPCa from BPD was 5.30 (sensitivity, 85.85%; specificity, 86.21%; area under the curve [AUC], 0.893). The cutoff achieved a sensitivity of 83.33%, a specificity of 81.25%, a positive predictive value (PPV) of 92.11%, a negative predictive value (NPV) of 65.00%, and an accuracy of 82.76% in the prospective validation cohort. Metastases were used as an indicator to reduce false negative results in patients with SUV_max ≤ 5.30. In patients without metastases, an SUV_max value of 5.30 was also the best cutoff to diagnose localized csPCa (sensitivity, 80.43%; specificity, 86.21%; AUC, 0.852). The cutoff discriminated localized csPCa from BPD with a sensitivity of 76.19%, a specificity of 81.25%, a PPV of 84.21%, an NPV of 72.22%, and an accuracy of 78.38% in the prospective validation cohort. The cutoff, combined with metastases, achieved an accuracy of 89.12% in all patients, increasing accuracy by 8.29% and reducing equivocal results compared with manual reading. There was a strong correlation between SUV_max and PSMA expression (r_s = 0.831, P < 0.001) and a moderate correlation between SUV_max and GS (r_s = 0.509, P < 0.001). The PSMA expression and SUV_max values of patients with csPCa were significantly higher than those of patients with BPD (P < 0.001).

Conclusion: We established and prospectively validated the best SUV_max cutoff value (5.30) for discriminating csPCa from BPD with high accuracy in patients with suspected PCa. 5.30 is an effective cutoff to discriminate csPCa patients with or without metastases. The cutoff may provide a potential tool for the precise identification of csPCa by ⁶⁸Ga-PSMA PET/CT, ensuring high accuracy and reducing equivocal results.

Evaluation of 68Ga-PSMA PET/CT with volumetric parameters for staging of prostate cancer patients

BACKGROUND

The aim of this study was to investigate the relationship between volumetric data obtained from staging 68Ga-prostate-specific membrane antigen (PSMA) PET computerized tomography (CT) images with prostate-specific antigen (PSA), risk groups, Gleason Grade (GG) groups and presence of metastasis.

METHODS

We performed a retrospective analysis of 68Ga-PSMA PET-CT images from 88 patients undergoing initial staging of prostate adenocarcinoma between January 2015 and September 2018. Images were evaluated in LIFEx software; PSMA involvement above the background activity in prostate gland, lymph node and other distant metastases was plotted with 40% SUVmax threshold, SUVmax, PSMA tumor volume (PSMA-TV) and total lesion PSMA (TL-PSMA) values were obtained.

RESULTS

In all patients, there was a moderate correlation between PSA and PSMA-tumor volume whole-body (PSMA-TVwb) (P < 0.001, r = 0.580) and a high correlation between total lesion-PSMAwb (TL-PSMAwb) (P < 0.001, r = 0.636). Prostate PSMA-TV (PSMA-TVp) and TL-PSMA (PSMA-TVp) values were different in local and locally advanced/metastatic patients (P = 0.020 and 0.006, respectively). PSMA-TVp and TL-PSMAp values were significantly different in low-moderate and high-risk patients (P = 0.003 and <0.001, respectively), and in patients with and without metastasis (P = 0.008 and <0.001, respectively). PSMA-TVp, PSMA-TVwb, TL-PSMAp and TL-PSMAwb values were significantly different in patients with GG ≤3 and >3 (P = 0.030, 0.002, <0.001 and <0.001, respectively).

CONCLUSION

Pretreatment 68Ga-PSMA PET/CT volumetric parameters provides unique data to use in the clinical decision-making process of patients with adenocarcinoma of the prostate.

Parameters predicting [18F]PSMA-1007 scan positivity and type and number of detected lesions in patients with biochemical recurrence of prostate cancer

BACKGROUND

Detection of the site of recurrence using PSMA-PET/CT is important to guide treatment in patients with biochemical recurrence of prostate cancer (PCa). The aim of this study was to evaluate the positivity rate of [¹⁸F]PSMA-1007-PET/CT in patients with biochemically recurrent PCa and identify parameters that predict scan positivity as well as the type and number of detected lesions. This monocentric retrospective study included 137 PCa patients with biochemical recurrence who underwent one or more [¹⁸F]PSMA-1007-PET/CT scans between August 2018 and June 2019. PET-positive malignant lesions were classified as local recurrence, lymph node (LN), bone or soft tissue lesions. The association between biochemical/paraclinical parameters, as PSA value, PSA doubling time, PSA velocity, Gleason score (GS) and androgen deprivation therapy (ADT), and scan positivity as well as type and number of detected lesions was evaluated using logistic regression analysis (binary outcomes) and Poisson models (count-type outcomes).

RESULTS

We included 175 [¹⁸F]PSMA-1007-PET/CT scans after radical prostatectomy (78%), external beam radiation therapy (8.8%), ADT (7.3%), brachytherapy (5.1%) and high intensity focused ultrasound (0.7%) as primary treatment (median PSA value 1.6 ng/ml). Positivity rate was 80%. PSA value and PSA velocity were significant predictors of scan positivity as well as of the presence of bone and soft tissue lesions and number of bone, LN and soft tissue lesions, both in uni- and/or multivariable analysis. Multivariable analysis also showed prior ADT as predictor of bone and soft tissue lesions, GS as predictor of the number of bone lesions and ongoing ADT as predictor of the number of LN lesions.

CONCLUSION

[¹⁸F]PSMA-1007-PET/CT showed a high positivity rate in patients with biochemically recurrent PCa. PSA value and PSA velocity were significant predictors of scan positivity as well as of the presence and number of bone and soft tissue lesions and the number of LN lesions. Our findings can guide clinicians in optimal patient selection for [¹⁸F]PSMA-1007-PET/CT and support further research leading to the development of a prediction nomogram.

Metastatic Spread in Prostate Cancer Patients Influencing Radiotherapy Response

Radiotherapy and surgery are curative treatment options for localized prostate cancer (PCa) with a 5-year survival rate of nearly 100%. Once PCa cells spread into distant organs, such as bone, the overall survival rate of patients drops dramatically. The metastatic cascade and organotropism of PCa cells are regulated by different cellular subtypes, organ microenvironment, and their interactions. This cross-talk leads to pre-metastatic niche formation that releases chemo-attractive factors enforcing the formation of distant metastasis. Biological characteristics of PCa metastasis impacting on metastatic sites, burden, and latency is of clinical relevance. Therefore, the implementation of modern hybrid imaging technologies into clinical routine increased the sensitivity to detect metastases at earlier stages. This enlarged the number of PCa patients diagnosed with a limited number of metastases, summarized as oligometastatic disease. These patients can be treated with androgen deprivation in combination with local-ablative radiotherapy or radiopharmaceuticals directed to metastatic sites. Unfortunately, the number of patients with disease recurrence is high due to the enormous heterogeneity within the oligometastatic patient population and the lack of available biomarkers with predictive potential for metastasis-directed radiotherapy. Another, so far unmet clinical need is the diagnosis of minimal residual disease before onset of clinical manifestation and/or early relapse after initial therapy. Here, monitoring of circulating and disseminating tumor cells in PCa patients during the course of radiotherapy may give us novel insight into how metastatic spread is influenced by radiotherapy and vice versa. In summary, this review critically compares current clinical concepts for metastatic PCa patients and discuss the implementation of recent preclinical findings improving our understanding of metastatic dissemination and radiotherapy resistance into standard of care.

Diagnostic value of 18F-FDG PET/CT in patients with biochemical recurrent prostate cancer and negative 68Ga-PSMA PET/CT

PURPOSE

⁶⁸Ga-PSMA PET/CT has a high detection rate in prostate cancer patients with biochemical recurrence (BCR). However, few studies have reported other imaging methods for BCR with negative ⁶⁸Ga-PSMA PET/CT findings. We investigated the value of ¹⁸F-FDG compared with ⁶⁸Ga-PSMA and identified BCR patients with ⁶⁸Ga-PSMA-negative findings who are most likely to benefit from ¹⁸F-FDG PET/CT.

METHODS

Seventy-two BCR patients with negative ⁶⁸Ga-PSMA PET/CT findings were retrospectively identified from 510 patients who underwent concomitant ⁶⁸Ga-PSMA and ¹⁸F-FDG PET/CT between June 2018 and August 2020. Patients were categorised into groups with positive or negative ¹⁸F-FDG PET/CT findings. Differences in patients' characteristics between these two groups and predictors of positive ¹⁸F-FDG findings were analysed.

RESULTS

The detection rate of ¹⁸F-FDG PET/CT was 16.7% (12/72) in BCR patients with ⁶⁸Ga-PSMA-negative findings. PSA and Gleason score were significantly higher in the ¹⁸F-FDG-positive group than in the ¹⁸F-FDG-negative group (P < 0.001 and P < 0.001, respectively). A multivariate analysis indicated that PSA (PSA ≥2.3 ng/mL) and Gleason score (Gleason score ≥ 8) correlated with ¹⁸F-FDG-positive findings (P < 0.001 and P = 0.015, respectively). The probabilities of ¹⁸F-FDG-positive findings in the low-potential (PSA <2.3 ng/mL and Gleason score <8), moderate-potential (PSA <2.3 ng/mL and Gleason score ≥ 8 or PSA ≥2.3 ng/mL and Gleason score <8), and high-potential (PSA ≥2.3 ng/mL and Gleason score ≥ 8) groups were 0%, 11.5%, and 90.0%, respectively (P < 0.001).

CONCLUSION

PSA level and Gleason score are independent predictors of ¹⁸F-FDG-positive findings, and BCR patients with ⁶⁸Ga-PSMA-negative findings with high PSA and Gleason score are most likely to benefit from ¹⁸F-FDG PET/CT.

Molecular pathology of prostate cancer: a practical approach

While localised prostate cancer can be cured by local treatment, 'high-risk' prostate cancer often progresses to castration resistant disease and remains incurable with a dismal prognosis. In recent years, technical advances and development of novel methodologies have largely contributed to a better understanding of underlying molecular mechanisms that promote tumour growth and progression. Consecutively, novel therapeutic strategies for treatment of prostate cancer have emerged during the last decade, calling for the identification of predictive biomarkers. The concept of personalised medicine is to tailor treatment according to the specific tumour profile of an individual patient. Moreover, acquired molecular changes during tumour evolution and in response to therapy selection pressure require adapted predictive marker testing at different time points during the disease. In this setting, the pathologist plays a critical role in patient management and treatment selection. In this review, we provide a comprehensive overview of the current knowledge of molecular aspects of prostate cancer and their potential utility in the context of different therapeutic approaches. Furthermore, we discuss methods for molecular marker testing in routine clinical practice, with a focus on castration resistant prostate cancer.