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

The role of PSMA-based radioligand therapy in hormone-sensitive prostate cancer

PURPOSE

Conventional systemic therapies are valuable options in prostate cancer (PCa); however, such treatments can determine adverse events and toxicity. The observed improvement in overall survival, coupled with PSA reduction and a favorable safety profile in the post-taxane castration-resistant PCa (CRPC) setting has prompted the consideration of PSMA-based radioligand therapy (RLT) earlier in the treatment sequence. In this review, we will describe the literature and ongoing clinical trials regarding the use of PSMA-based RLT in hormone-sensitive PCa (HSPC) including the neoadjuvant, de-novo/synchronous metastatic, adjuvant, and early BCR settings.

METHODS

We performed a systematic literature search on the PubMed/MEDLINE/EMBASE and clinicaltrials.gov databases for studies and protocols assessing the role of PSMA-based RLT in HSPC.

RESULTS

The literature search yielded 140 results. After screening titles and abstracts and applying inclusion and exclusion criteria, we selected 25 papers showing the potentialities of earlier RLT in HSPC, with several ongoing trials.

CONCLUSION

Early use of PSMA-based RLT holds significant potential in HSPC patients from the neoadjuvant to the BCR setting. In these stages, the lower tumor burden, more frequent exclusive nodal involvement, and higher organ reserve may improve treatment efficacy and allow for treatment combinations while maintaining a less toxic profile.

Multitracer comparison of gold standard PSMA-PET/CT with 68Ga-FAPI and 18F-FDG in high-risk prostate cancer: a proof-of-concept study

PURPOSE

The aim of this study was to, evaluate the diagnostic accuracy of [⁶⁸Ga]Ga-FAPI-46 positron emission tomography (PET)/computed tomography (CT) in high-risk prostate cancer (PC) compared to [¹⁸F]PSMA / [⁶⁸Ga]Ga- PSMA- and [¹⁸F]FDG- PET/CT as well as multiparametric magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Ten patients with high-risk PC (PSA > 20 ng/mL, Gleason score > 7, or > T2c) underwent PET/CT imaging using [⁶⁸Ga]Ga-FAPI-46, [¹⁸F]F-/[⁶⁸Ga]Ga-PSMA and [¹⁸F]FDG before radical prostatectomy (RP). The maximum standardized uptake values (SUVmax) were measured for the entire prostate and individual prostate sextants. Diagnostic accuracy was assessed per patient and per segment by correlating imaging findings with final histopathologic results. Immunohistochemical analysis of PSMA and FAP expression was performed on the index tumor lesion.

RESULTS

Histopathologic analysis confirmed pT2c and pT3 prostate adenocarcinoma in 4 (40%) and 6 (60%) patients, respectively. One patient (10%) had regional lymph node metastasis (pN1). The International Society of Urological Pathology (ISUP) grade groups (GGs) were 2 (60%), 3 (20%), and 5 (20%). Overall, 46 of 60 prostate sextants were histologically positive for PC. While PSMA expression was detected in all patients, FAP expression was observed in 5 of 9 cases (55.5%). Per-patient and per-segment analyses demonstrated that [⁶⁸Ga]Ga-FAPI-46 and [¹⁸F]F-/[⁶⁸Ga]Ga-PSMA had comparable diagnostic accuracy and outperformed [¹⁸F]FDG. The mean (SD) SUVmax of the entire prostate was highest for PSMA PET/CT at 13.1 (7), followed by FAPI at 7.6 (5.5) and FDG at 5.4 (3.5) (p = 0.015). Among patients in the FAPI subgroup, those with ISUP GG 3-5 exhibited greater FAP expression and radiotracer uptake compared to ISUP GG 2 cases. In the two high-grade patients, [⁶⁸Ga]Ga-FAPI-46 demonstrated greater tumor uptake than [¹⁸F]PSMA / [⁶⁸Ga]Ga-PSMA PET/CT. Notably, MRI demonstrated higher diagnostic accuracy and superior local staging compared to all radiotracers evaluated.

CONCLUSION

FAP expression was detected in a subset of high-risk PC patients, particularly in those with higher-grade disease. This proof-of-concept study may suggest a role for [⁶⁸Ga]Ga-FAPI-46 PET/CT in primary PC with low PSMA avidity, but further research is warranted to define its clinical application.

Prevalence and Medium-Term Outcomes of Patients with Biopsy-Proven Intermediate- to High-Risk Prostate Adenocarcinoma with Low Intraprostatic Uptake on [68Ga]Ga-PSMA-11 PET/CT in the proPSMA Study

The current prevalence of low intraprostatic uptake for staging prostate-specific membrane antigen (PSMA) PET ranges between 4.4% and 17% in retrospective studies. We aimed to define the prevalence and describe the outcomes of patients with low intraprostatic uptake on PSMA PET/CT in the prospective proPSMA study. Methods: We identified patients with an SUVmax of 4 or less on PSMA PET/CT in the proPSMA study. Patients were followed up until 42 mo after randomization. The PRIMARY score was evaluated by 3 nuclear medicine physicians, with the result determined by consensus. Treatment failure was defined as new metastatic disease, biochemical recurrence, or initiation of salvage therapy. Results: Ten of 302 (3.3%; 95% CI, 1.6%-6.0%) patients had low intraprostatic uptake on PSMA PET/CT and normal findings on conventional imaging (CT and whole-body bone scanning). The median age was 66 y (interquartile range, 60.5-70.3 y). International Society of Urological Pathologists biopsy grade group was 3 in 5 patients and 5 in 5 patients, with no atypical histology identified. The median prostate-specific antigen level was 5.1 ng/nL (interquartile range, 2.3-8.3 ng/nL). The median follow-up interval was 30 mo (interquartile range, 24-39 mo). Multiparametric MRI was performed on 5 patients, with Prostate Imaging-Reporting and Data System score 5 in 2 patients, 4 in 1 patient, and 2 in 2 patients. The PRIMARY score was positive in 5 of 10 (50%) patients. Five (50%), 4 (30%), and 2 (20%) of 10 patients received radical prostatectomy, definitive radiotherapy, and androgen deprivation therapy alone, respectively. Of the 9 (90%) patients who received definitive treatment, 1 (11%) experienced treatment failure at 18 mo after radical prostatectomy and received metastasis-directed therapy. Biochemical recurrence was nonevaluable in the single patient who received androgen deprivation therapy alone. At the 42-mo follow-up after randomization, 4 of 9 (44%) patients who received definitive therapy remained on trial-none of whom had evidence of treatment failure. No other patients had new metastatic disease or initiation of salvage therapy during follow-up. Conclusion: In the proPSMA trial, there was a low prevalence (3.3%) of low intraprostatic uptake on PSMA PET/CT in patients with biopsy-confirmed prostate cancer, and treatment failure was infrequent.

How Prostate Cancer Growth Patterns Impact Detection and Interreader Agreement on Multiparametric MRI

RATIONALE AND OBJECTIVES

Multiparametric MRI (mpMRI) substantially improves the detection of significant prostate carcinoma (PCa) compared to systematic biopsy. Nevertheless, mpMRI can overlook aggressive forms of PCa. Recent studies showed, that infiltrative growth (INF) has less restricted diffusion. This study aims to explore the impact of growth patterns on the detection of lesions.

MATERIALS AND METHODS

This retrospective study analyzed 52 patients who underwent radical prostatectomy, with preoperative mpMRI. For each patient, one dominant lesion was identified on one whole-mount prostatectomy section. Two pathologists (P1, P2) independently classified the growth pattern whether as expansive (EXP) being defined with at least three 5mm² regions of interest consisting entirely of carcinoma without benign glands or else as infiltrative (INF). Two radiologists (R1, R2) independently classified selected lesions according to PI-RADSv2.1. based on pathological localization. Apparent diffusion coefficient (ADC) values were measured in correlation with matched histopathology slides. Interreader-agreement was evaluated using weighted Cohen's Kappa. The relationship between PI-RADS scores and pathological diagnoses was analyzed using logistic regression.

RESULTS

Pathologic lesion characterization regarding growth patterns achieved almost perfect agreement (κ = 0.88), so did PI-RADS classification of mpMRI (κ = 0.90). PI-RADS scores correlated significantly with EXP growth patterns. Average ADC values were lower for EXP lesions (0.83×10-3 mm2/s, CI: 0.72-0.94×10-3 mm2/s) compared to INF lesions (0.97×10-3 mm2/s, CI: 0.86-1.07×10-3 mm2/s; p = 0.08). On T2 images, 8 of 28 (29%) INF lesions and 1 of 24 (4%) EXP lesions were not visible.

CONCLUSION

PCa missed on mpMRI more frequently demonstrate INF growth patterns. Lesions with EXP growth patterns show lower ADC values and have higher PI-RADS scores.

Can PSMA PET detect intratumour heterogeneity in histological PSMA expression of primary prostate cancer? Analysis of [68Ga]Ga-PSMA-11 and [18F]PSMA-1007

PURPOSE

Prostate-specific membrane-antigen positron emission tomography (PSMA PET) is a promising candidate for non-invasive characterization of prostate cancer (PCa). This study evaluated whether PET with tracers [68Ga]Ga-PSMA-11 or [18F]PSMA-1007 is capable to depict intratumour heterogeneity of histological PSMA expression.

METHODS

Thirty-five patients with biopsy-proven primary PCa without evidence of metastatic disease nor prior interventions were prospectively enrolled. All patients underwent PSMA PET combined with computer tomography (CT) with either [68Ga]Ga-PSMA-11 (cohort I, 20 patients) or [18F]PSMA-1007 (cohort II, 15 patients) followed by radical prostatectomy. Specimens were scanned by ex-vivo CT and histologically prepared. On digitized whole-mount prostate sections, PCa areas with different morphologies were manually defined and H-Score of immunohistochemical PSMA expression was calculated with assistance by artificial intelligence (AI). PCa areas with similar H-Score were unified in segmentation on ex-vivo CT. After co-registration on PSMA PET-CT, Spearman's coefficients of PSMA expression to mean and maximum standardized uptake value (SUVmean and SUVmax) were calculated. Furthermore, the agreement of the co-registered tumour areas to gross tumour volume (GTV) in PSMA PET was analysed.

RESULTS

Thirty-two patients were included in the final analysis. For histological PCa areas, immunohistochemical PSMA expression correlated significantly to SUVmean and SUVmax (p < 0.001, p = 0.001). An approximate linear correlation between H-Score and SUVmean / SUVmax was found for tumour areas larger than 400 μm² in histology (p < 0.001). Tumour areas with strong PSMA expression showed a significantly larger overlap to GTV in PSMA PET after co-registration than tumour areas with very low PSMA expression (p < 0.01). No significant differences were found between the two tracer cohorts (p = 0.72).

CONCLUSION

PSMA PET with both [68Ga]Ga-PSMA-11 or [18F]PSMA-1007 is able to detect changes in histological PSMA expression within PCa lesions allowing biologically targeted radiotherapy.

Immunohistochemical Prostate-specific Membrane Antigen (PSMA) Expression Patterns of Primary Prostate Cancer Tissue as a Determining Factor for Prostate Cancer Staging with PSMA Positron Emission Tomography/Computed Tomography

BACKGROUND AND OBJECTIVE

In recent studies, prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) has shown accuracy in staging patients diagnosed with prostate cancer. Here, we aim to evaluate the correlation between PSMA immunohistochemical characteristics of prostate cancer (PCa)-positive biopsy cores and whole-mount specimens, and test the predictive role of PSMA expression in biopsy samples for staging PSMA PET/CT.

METHODS

A total of 104 patients with high- or intermediate-risk PCa who underwent [68Ga]Ga-PSMA-11 PET/CT before radical prostatectomy were prospectively selected between June 2021 and July 2023. The analysis of immunohistochemical PSMA expression was performed using the Immunoreactive Score (IRS). The correlation between biopsy and final specimen was evaluated using Gwet's agreement coefficient for ordinal variables (AC1). Regression models tested the immunohistochemical PSMA expression in biopsy/vesicoprostatic block and the PSMA PET/CT maximum standardized uptake value (SUVmax).

KEY FINDINGS AND LIMITATIONS

A statistically significant strong correlation was found between PSMA expression in biopsy and vesicoprostatic block (AC1 = 0.8 [confidence interval {CI} 0.7-0.9], p < 0.01). According to the multivariable linear regression models, the IRSs of both the PCa-positive biopsy cores and the index lesion were statistically significant predictors of SUVmax (β = 3.3, CI 1.5-7.5, p < 0.01 and β = 4.9, CI 1.8-13, p < 0.01, respectively). Limitations include manual interpretation of immunohistochemistry, potential model overfitting, and a short follow-up.

CONCLUSIONS AND CLINICAL IMPLICATIONS

The immunohistochemical analysis of PSMA expression in PCa-positive biopsy cores showed a high correlation with the whole-mount specimen. The degree of PSMA expression is an independent predictor of SUVmax. The assessment of immunohistochemical PSMA expression in a preoperative setting may have implications for determining a more accurate, patient-specific diagnostic pathway.

Prospective comparison of 18F-PSMA-1007 PET/CT and MRI with histopathology as the reference standard for intraprostatic tumour detection and T-staging of high-risk prostate cancer

PURPOSE

To prospectively compare the ability of 18F-PSMA-1007 PET/CT and whole-body MRI (WBMRI) with DWI to detect prostate cancer (PCa) lesions and assess their local stage. Additionally, to evaluate the correlation between PSMA uptake on PET/CT and PSMA expression as assessed by immunohistochemistry.

METHODS

Men with newly diagnosed unfavourable intermediate or high-risk PCa underwent 18F-PSMA-1007 PET/CT and WBMRI with DWI before robot-assisted laparoscopic prostatectomy. Diagnostic accuracy for intraprostatic tumour localization, seminal vesicle invasion (SVI), and extraprostatic extension (EPE) was evaluated using whole-mount prostatectomy specimens as the reference standard. SUVmax was compared with immunohistochemical PSMA staining intensity quantified using QuPath software.

RESULTS

19 patients with 39 intraprostatic lesions in histopathology were included. The overall lesion detection rates for PET/CT were 84.6% and 82.1% for two independent readers, compared to 74.4% and 46.2% for MRI readers. The detection rates of index lesions were 94.7% for PET/CT and 74.0-84.0% for MRI, whereas those of non-index lesions were 70.0-75.0% for PET/CT and 20.0-65.0% for MRI. For detecting EPE, AUC values were 0.500-0.591 for PET/CT and 0.648-0.682 for MRI. For detecting SVI, AUC values ranged from 0.629 to 0.700 across both modalities. SUVmax showed a weak correlation with immunohistochemical expression of PSMA multiplied by lesion diameter (Spearman's ρ = 0.427, p = 0.013). Lesion diameters measured using 30% and 40% of SUVmax, as well as prostate SUVbackground x2, showed the closest agreement with histopathological measurements.

CONCLUSION

18F-PSMA-1007 PET/CT demonstrated high sensitivity in localizing intraprostatic carcinoma lesions but seemed inferior to WBMRI in detecting EPE. PSMA uptake appears to depend on both PSMA expression and lesion size. These findings highlight the complementary roles of PET/CT and MRI in the detection and tumor staging of PCa.

CLINICAL TRIAL REGISTRATION

Clinicaltrials.gov ID: NCT03537391. Registered 25 May 2018.

Real-time diagnosis of sampled lesions in targeted biopsy of prostate Cancer using a novel tracer [64Cu] Cu-DOTA-PSMA-3Q: a pilot preclinical study

PURPOSE

Prostate-specific membrane antigen positron emission tomography (PSMA-PET) guided targeted biopsy has shown potential for detecting more prostate cancer (PCa) cases. However, relying exclusively on imaging may risk missing lesions, an issue that could be addressed by incorporating radiation-guided technology. Accordingly, we aimed to develop a novel PSMA radiotracer with a long half-life, [64Cu]Cu-DOTA-PSMA-3Q, and evaluate its targeting accuracy. Additionally, this research explored the practicability of real-time lesion verification during surgical interventions.

METHODS

In this study, we synthesized the radiotracer [64Cu]Cu-DOTA-PSMA-3Q and verified its PSMA specificity and safety. We prospectively enrolled 18 patients with suspected PCa for PET/CT imaging to assess the efficacy of PCa detection; 10 patients underwent targeted biopsy combined with standard template biopsy at an interval of 24 h after injection. The radioactivity of the biopsy tissue was quantified in counts per minute (CPM) using a gamma spectrometer intraoperatively.

RESULTS

The efficacy and specificity of [64Cu]Cu-DOTA-PSMA-3Q were confirmed through preclinical cell and animal studies. In clinical settings, PET/CT imaging performed 2 h after injection visualized all of the PSMA-positive lesions both within and outside the prostate. The assessment of human organ radiation exposure indicated that the kidneys received the highest absorbed dose, followed by the bladder wall, salivary glands, and liver. In 10 patients, a total of 132 biopsy cores were extracted, with 53 cores histologically confirmed as PCa. The median CPM for PCa tissues was significantly greater at 134,148 CPM compared to 18,39 CPM for normal prostate tissues (P < 0.001). Receiver operating characteristic (ROC) curve analysis yielded an AUC of 0.8837, suggesting high diagnostic accuracy. The optimal diagnostic cut-off was established at 66 CPM, achieving a sensitivity of 77.36%.

CONCLUSIONS

Radiation-guided technology using [64Cu]Cu-DOTA-PSMA-3Q improves the reliability of PSMA-PET image-guided biopsy, enables instant confirmation of sample lesions during surgical procedures, and holds potential for achieving optimized puncture outcomes.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ChiCTR2300072655, Registered 20 June 2023.

Comparison of PSMA immunohistochemistry scoring systems to parametric [18F]PSMA-1007 PET/MRI in primary prostate cancer

PURPOSE

Quantification of PSMA expression via PSMA PET is well-established, however quantification of PSMA via immunohistochemistry (IHC) is not standardized. Our aim was to determine the most optimal PSMA IHC scoring system to quantify PSMA expression with PSMA PET as reference standard.

METHODS

Primary intermediate- and high-risk prostate cancer patients received an [18F]PSMA-1007 PET/MRI followed by radical prostatectomy. SUVmax, SUVmean and Ki of the prostate tumor was determined. Prostate tumors were stained with anti-PSMA antibodies and scored by 2 readers via 10 IHC scoring systems: histochemical score (H-score), immunoreactivity scorepredominant intensity (IRSpredominant intensity), IRS classificationpredominant intensity, IRSmean intensity, IRS classificationmean intensity, Allred score, predominant expression pattern, Shannon diversity index (SDI), percentage negatively stained cells and total percentage positively stained cells. Spearman's rank correlation coefficients (ρ) were calculated between PET parameters and IHC scoring systems. Interreader agreement for the IHC scoring systems was measured by the intraclass correlation coefficient (ICC).

RESULTS

Fifty tumors in 46 patients were analysed. H-score had the best correlation with SUVmax (ρ 0.615 p < 0.0001) and SUVmean (ρ 0.570, p < 0.0001) and the second best correlation with Ki (ρ 0.411, p = 0.0030). SDI had the best correlation with Ki (ρ -0.440, p = 0.0014) and the second best correlation with SUVmax (ρ -0.516, p = 0.0001) and SUVmean (ρ -0.490, p = 0.0003). A moderate interreader agreement was observed for H-score (ICC 0.663, 95% CI 0.495-0.797) and SDI (ICC 0.546, 95% CI 0.354-0.725).

CONCLUSION

H-score had the best correlation with PSMA PET quantification and an acceptable interreader agreement. Therefore, we deem H-score the most optimal PSMA IHC scoring system.

FAP and PSMA Expression by Immunohistochemistry and PET Imaging in Castration-Resistant Prostate Cancer: A Translational Pilot Study

Prostate-specific membrane antigen (PSMA) is a theranostic target for metastatic prostate cancer (PCa). However, castration-resistant PCa (CRPC) may lose PSMA expression after systemic therapy. Fibroblast activation protein (FAP), expressed by carcinoma-associated fibroblasts in various cancer types, including PCa, has the potential to be an alternative target. In this study, we evaluated FAP expression in CRPC to assess its potential, using PSMA as a comparison. Methods: FAP expression was assessed using immunohistochemistry in 116 CRPC tumors: 78 adenocarcinomas, 11 small cell carcinomas, and 27 anaplastic carcinomas. Correlation analysis between manual scoring and automated scoring was performed on 54 whole-slide sections of metastatic CRPC. Paired FAP and PSMA stains were assessed in tissue microarray cores of CRPC (n = 62), consisting of locally advanced CRPC (n = 9) and metastatic CRPC (n = 53). FAP and PSMA positivity was defined by an immunohistochemistry score of at least 10. To explore the correlation of PSMA and FAP inhibitor (FAPi) PET imaging and immunohistochemistry, a preliminary analysis of 4 patients included in a [68Ga]-FAPi-46 imaging trial (NCT04457232) was conducted. Results: Manual and automated scoring of FAP yielded results with strong correlations. Overall, FAP expression in CRPC was notably lower than PSMA expression (median immunoscores, 14 vs. 72; P < 0.001). Different histologic subtypes of CRPC demonstrated distinct levels of PSMA expression, whereas their FAP expression levels were comparable. Among the 19 PSMA-negative tumors, 11 (58%) exhibited FAP positivity. FAP expression levels in lymph node metastases were significantly lower than those in nonnodal metastases (P = 0.021). Liver metastases showed significant enrichment of tumors with strong FAP expression compared with nonliver lesions (P = 0.016). In the 4 clinical trial patients, the biopsied metastatic lesions showed lower uptake on FAPi PET than on PSMA PET (median SUVmax, 9.6 vs. 14.5), consistent with FAP expression that was lower than PSMA expression in the corresponding tumor biopsy samples (median immunoscores, 30 vs. 160). Conclusion: Because of the low FAP expression levels in CRPC, the utility of FAPi PET imaging may be limited. Although FAPi PET imaging may be further tested in PSMA-negative CRPC, such as small cell carcinoma, other molecular imaging modalities should be evaluated as alternative choices.

Immunohistochemical ERG positivity is associated with decreased PSMA expression and lower visibility in corresponding [68Ga]Ga-PSMA-11 PET scans of primary prostate cancer

PURPOSE

TMPRSS2:ERG gene fusion negatively regulates PSMA expression in prostate adenocarcinoma (PCa) cell lines. Therefore, immunohistochemical (IHC) ERG expression, a surrogate for an underlying ERG rearrangement, and PSMA expression patterns in radical prostatectomy (RPE) specimens of primary PCa, including corresponding PSMA-PET scans were investigated.

METHODS

Two cohorts of RPE samples (total n=148): In cohort #1 (n=62 patients) with available RPE and preoperative [68Ga]Ga-PSMA-11 PET, WHO/ISUP grade groups, IHC-ERG (positive vs. negative) and IHC-PSMA expression (% PSMA-negative tumour area, PSMA%neg) were correlated with the corresponding SUVmax. In the second cohort #2 (n=86 patients) including RPE only, same histopathological parameters were evaluated.

RESULTS

Cohort #1: PCa with IHC-ERG expression (35.5%) showed significantly lower IHC-PSMA expression and lower SUVmax values on the corresponding PET scans. Eight of 9 PCa with negative PSMA-PET scans had IHC-ERG positivity, and confirmed TMPRSS2::ERG rearrangement. In IHC-PSMA positive PCa, IHC-ERG positivity was significantly associated with lower SUVmax values. In cohort #2, findings of higher IHC-PSMA%neg and IHC-ERG expression was confirmed with only 0-10% PSMA%neg tumour areas in IHC-ERG-negative PCa.

CONCLUSION

IHC-ERG expression is significantly associated with more heterogeneous and lower IHC-PSMA tissue expression in two independent RPE cohorts. There is a strong association of ERG positivity in RPE tissue with lower [68Ga]Ga-PSMA-11 uptake on corresponding PET scans. Results may serve as a base for future biomarker development to enable tumour-tailored, individualized imaging approaches.

Biology-guided radiotherapy in metastatic prostate cancer: time to push the envelope?

The therapeutic landscape of metastatic prostate cancer has undergone a profound revolution in recent years. In addition to the introduction of novel molecules in the clinics, the field has witnessed a tremendous development of functional imaging modalities adding new biological insights which can ultimately inform tailored treatment strategies, including local therapies. The evolution and rise of Stereotactic Body Radiotherapy (SBRT) have been particularly notable in patients with oligometastatic disease, where it has been demonstrated to be a safe and effective treatment strategy yielding favorable results in terms of disease control and improved oncological outcomes. The possibility of debulking all sites of disease, matched with the ambition of potentially extending this treatment paradigm to polymetastatic patients in the not-too-distant future, makes Biology-guided Radiotherapy (BgRT) an attractive paradigm which can be used in conjunction with systemic therapy in the management of patients with metastatic prostate cancer.

Metabolic imaging across scales reveals distinct prostate cancer phenotypes

Hyperpolarised magnetic resonance imaging (HP-13C-MRI) has shown promise as a clinical tool for detecting and characterising prostate cancer. Here we use a range of spatially resolved histological techniques to identify the biological mechanisms underpinning differential [1-13C]lactate labelling between benign and malignant prostate, as well as in tumours containing cribriform and non-cribriform Gleason pattern 4 disease. Here we show that elevated hyperpolarised [1-13C]lactate signal in prostate cancer compared to the benign prostate is primarily driven by increased tumour epithelial cell density and vascularity, rather than differences in epithelial lactate concentration between tumour and normal. We also demonstrate that some tumours of the cribriform subtype may lack [1-13C]lactate labelling, which is explained by lower epithelial lactate dehydrogenase expression, higher mitochondrial pyruvate carrier density, and increased lipid abundance compared to lactate-rich non-cribriform lesions. These findings highlight the potential of combining spatial metabolic imaging tools across scales to identify clinically significant metabolic phenotypes in prostate cancer.

Multiparametric Whole-Body MRI: A Game Changer in Metastatic Prostate Cancer

Prostate cancer ranks among the most prevalent tumours globally. While early detection reduces the likelihood of metastasis, managing advanced cases poses challenges in diagnosis and treatment. Current international guidelines support the concurrent use of 99Tc-Bone Scintigraphy and Contrast-Enhanced Chest and Abdomen CT for the staging of metastatic disease and response assessment. However, emerging evidence underscores the superiority of next-generation imaging techniques including PSMA-PET/CT and whole-body MRI (WB-MRI). This review explores the relevant scientific literature on the role of WB-MRI in metastatic prostate cancer. This multiparametric imaging technique, combining the high anatomical resolution of standard MRI sequences with functional sequences such as diffusion-weighted imaging (DWI) and bone marrow relative fat fraction (rFF%) has proved effective in comprehensive patient assessment, evaluating local disease, most of the nodal involvement, bone metastases and their complications, and detecting the increasing visceral metastases in prostate cancer. It does have the advantage of avoiding the injection of contrast medium/radionuclide administration, spares the patient the exposure to ionizing radiation, and lacks the confounder of FLARE described with nuclear medicine techniques. Up-to-date literature regarding the diagnostic capabilities of WB-MRI, though still limited compared to PSMA-PET/CT, strongly supports its widespread incorporation into standard clinical practice, alongside the latest nuclear medicine techniques.

Negative biopsy histology in men with PI-RADS score 5: is it useful PSMA PET/CT evaluation?

INTRODUCTION

To evaluate the accuracy of PSMA PET/CT in men with mpMRI PI-RADS score 5 negative biopsy histology.

MATERIALS AND METHODS

From January 2011 to January 2023, 180 men with PI-RADS score 5 underwent systematic plus mpMRI/TRUS biopsy; 25/180 (13.9%) patients had absence of cancer and six months from biopsy were submitted to: digital rectal examination, PSA and PSA density exams, mpMRI and 68GaPSMA PET/CT evaluation (standardized uptake value "SUVmax" was reported).

RESULTS

In 24/25 (96%) patients PSA and PSA density significantly decreased, moreover, the PI-RADS score was downgraded resulting < 3; in addition, median SUVmax was 7.5. Only 1/25 (4%) man had an increased PSA value (from 10.5 to 31 ng/ml) with a confirmed PI-RADS score 5, SUVmax of 32 and repeated prostate biopsy demonstrating a Gleason score 9/ISUP Grade Group 5 PCa.

CONCLUSIONS

The strict follow up of men with PI-RADS score 5 and negative histology reduce the risk of missing csPCa especially if PSMA PET/CT evaluation is in agreement with downgrading of mpMRI (PI-RADS score < 3).

Evaluation of gastrin-releasing peptide receptor, prostate-specific membrane antigen, and neurotensin receptor 1 as potential biomarkers for accurate prostate cancer stratified diagnosis

BACKGROUND

Studies on single-target PET imaging of gastrin-releasing peptide receptor (GRPR), prostate-specific membrane antigen (PSMA), or neurotensin receptor 1(NTR1) have been reported. However, the performance of these three targets in the progression of PCa remains unclear. Our study aims to compare the expression of GRPR, PSMA, and NTR1 in patients with prostatic intraepithelial neoplasia (PIN), prostate cancer (PCa), and lymph node metastasis. We synthesized molecular probes targeting the markers to achieve a non-invasive precise detection of PCa patients with PET/CT imaging.

METHODS

In this study, the expression of GRPR, PSMA, and NTR1 was evaluated by immunohistochemistry in 34 PIN, 171 PCa, and 22 lymph node metastasis tissues of patients. The correlation between their expression and the clinicopathological parameters of PCa patients was assessed. Sixteen PCa patients with different Gleason scores (GS) underwent dual-tracer (68Ga-NOTA-RM26 and 68Ga-NOTA-PSMA617) PET/CT.

RESULTS

In the PIN stage, the expression of GRPR was significantly higher than that of PSMA and NTR1 (P < 0.001), while NTR1 expression was significantly higher than PSMA and GRPR expression in primary PCa (P = 0.001). High PSMA expression in PCa patients was associated with shorter progression-free survival (P = 0.037) and overall survival (P = 0.035). PCa patients with high GS had higher tumor uptake of 68Ga-NOTA-PSMA617 than those with low GS (P = 0.001), while PCa patients with low GS had higher tumor uptake of 68Ga-NOTA-RM26 than those with high GS (P = 0.001).

CONCLUSIONS

This study presents three novel biomarkers (PSMA, GRPR, and NTR1) as imaging agents for PET/CT, and may offer a promising approach for non-invasive precise detection and Gleason grade prediction of PCa patients.

PSMA-positive prostatic volume prediction with deep learning based on T2-weighted MRI

PURPOSE

High PSMA expression might be correlated with structural characteristics such as growth patterns on histopathology, not recognized by the human eye on MRI images. Deep structural image analysis might be able to detect such differences and therefore predict if a lesion would be PSMA positive. Therefore, we aimed to train a neural network based on PSMA PET/MRI scans to predict increased prostatic PSMA uptake based on the axial T2-weighted sequence alone.

MATERIAL AND METHODS

All patients undergoing simultaneous PSMA PET/MRI for PCa staging or biopsy guidance between April 2016 and December 2020 at our institution were selected. To increase the specificity of our model, the prostatic beds on PSMA PET scans were dichotomized in positive and negative regions using an SUV threshold greater than 4 to generate a PSMA PET map. Then, a C-ENet was trained on the T2 images of the training cohort to generate a predictive prostatic PSMA PET map.

RESULTS

One hundred and fifty-four PSMA PET/MRI scans were available (133 [68Ga]Ga-PSMA-11 and 21 [18F]PSMA-1007). Significant cancer was present in 127 of them. The whole dataset was divided into a training cohort (n = 124) and a test cohort (n = 30). The C-ENet was able to predict the PSMA PET map with a dice similarity coefficient of 69.5 ± 15.6%.

CONCLUSION

Increased prostatic PSMA uptake on PET might be estimated based on T2 MRI alone. Further investigation with larger cohorts and external validation is needed to assess whether PSMA uptake can be predicted accurately enough to help in the interpretation of mpMRI.

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.

Strong Correlation Between SUVmax on PSMA PET/CT and Numeric Drop-In γ-Probe Signal for Intraoperative Identification of Prostate Cancer Lesions

Prostate-specific membrane antigen (PSMA) PET is used to select patients with recurrent prostate cancer for metastasis-directed therapy. A surgical approach can be achieved through radioguided surgery (RGS), using a Drop-In γ-probe that traces lesions that accumulate the radioactive signal. With the aim of guiding patient selection for salvage surgery, we studied the correlation between the SUVmax of lesions on preoperative PSMA PET/CT and their intraoperative counts/s measured using the Drop-In γ-probe. Methods: A secondary analysis based on the prospective, single-arm, and single-center feasibility study was conducted (NCT03857113). Patients (n = 29) with biochemical recurrence after previous curative-intent therapy and a maximum of 3 suggestive lesions within the pelvis on preoperative PSMA PET/CT were included. Patients treated with androgen deprivation therapy within 6 mo before surgery were excluded. All patients received an intravenous injection of 99mTc-PSMA-I&S 1 d before surgery. Radioguidance was achieved using a Drop-In γ-probe. Correlation was determined using the Spearman rank correlation coefficient (ρs). Subgroup analysis was based on the median SUVmax Results: In total, 33 lesions were visible on the PSMA PET/CT images, with a median overall SUVmax of 6.2 (interquartile range [IQR], 4.2-9.7). RGS facilitated removal of 31 lesions. The median Drop-In counts/s were 134 (IQR, 81-220) in vivo and 109 (IQR, 72-219) ex vivo. The intensity of the values correlated with SUVmax (ρs = 0.728 and 0.763, respectively; P < 0.001). Subgroup analysis based on median SUVmax in the group with an SUVmax of less than 6 showed no statistically significant correlation with the numeric signal in vivo (ρs = 0.382; P = 0.221) or the signal-to-background-ratio (ρs = 0.245; P = 0.442), whereas the group with an SUVmax of 6 or more showed respective statistically significant positive correlations (ρs = 0.774 [P < 0.001] and ρs = 0.647 [P = 0.007]). Conclusion: Our findings indicate that there is a direct relation between SUVmax on PSMA PET/CT and the readout recorded by the surgical Drop-In probe, thereby indicating that SUVmax can be used to select patients for PSMA RGS. For more definitive subgroup definitions for treatment recommendations, further studies are necessary to validate the present findings.

Diagnostic performance of 18F‑DCFPyL PET vs. 68Ga‑PSMA PET/CT in patients with suspected prostate cancer: A systemic review and meta‑analysis

In this systematic review and meta-analysis, the diagnostic performance of 68Ga-prostate-specific membrane antigen (PSMA) positron emission tomography (PET)/CT was compared with that of 18F-DCFPyL PET for patients with suspected prostate cancer (PCa). Up to September 2023, the PubMed, Embase and Web of Science databases were thoroughly searched for relevant papers. Studies examining the diagnostic performance of 18F-DCFPyL PET and 68Ga-PSMA PET/CT in patients with suspected PCa were included in the present review. The Quality Assessment of Diagnostic Performance Studies-2 tool was used to rate the diagnostic performance of each study. The diagnostic performance of 18F-DCFPyL PET and 68Ga-PSMA PET/CT for primary PCa was examined by 13 studies included, comprising 1,178 patients. The pooled sensitivity and specificity of 18F-DCFPyL PET were 0.92 (95% CI, 0.85-0.96) and 0.59 (95% CI, 0.08-0.96), respectively. For 68Ga-PSMA PET/CT, the pooled sensitivity and specificity were 0.96 (95% CI, 0.88-0.99) and 0.71 (95% CI, 0.57-0.82), respectively. 18F-DCFPyL PET and 68Ga-PSMA PET/CT both had an area under the receiver operating characteristic curve of 0.92 (95% CI, 0.89-0.94). In addition, the Fagan nomogram revealed that the post-test probabilities for 18F-DCFPyL PET and 68Ga-PSMA PET/CT could rise to 69 and 77% when the pre-test probability was set at 50%. In conclusion, a comparable diagnostic performance for patients with suspected PCa was determined for 18F-DCFPyL PET and 68Ga-PSMA PET/CT. However, it is crucial to keep in mind that the findings of the present meta-analysis come from investigations with modest sample sizes. Therefore, more extensive research is required to obtain more solid data.

A convolutional neural network-based system for fully automatic segmentation of whole-body [68Ga]Ga-PSMA PET images in prostate cancer

PURPOSE

The aim of this study was development and evaluation of a fully automated tool for the detection and segmentation of mPCa lesions in whole-body [68Ga]Ga-PSMA-11 PET scans by using a nnU-Net framework.

METHODS

In this multicenter study, a cohort of 412 patients from three different center with all indication of PCa who underwent [68Ga]Ga-PSMA-11 PET/CT were enrolled. Two hundred cases of center 1 dataset were used for training the model. A fully 3D convolutional neural network (CNN) is proposed which is based on the self-configuring nnU-Net framework. A subset of center 1 dataset and cases of center 2 and center 3 were used for testing of model. The performance of the segmentation pipeline that was developed was evaluated by comparing the fully automatic segmentation mask with the manual segmentation of the corresponding internal and external test sets in three levels including patient-level scan classification, lesion-level detection, and voxel-level segmentation. In addition, for comparison of PET-derived quantitative biomarkers between automated and manual segmentation, whole-body PSMA tumor volume (PSMA-TV) and total lesions PSMA uptake (TL-PSMA) were calculated.

RESULTS

In terms of patient-level classification, the model achieved an accuracy of 83%, sensitivity of 92%, PPV of 77%, and NPV of 91% for the internal testing set. For lesion-level detection, the model achieved an accuracy of 87-94%, sensitivity of 88-95%, PPV of 98-100%, and F1-score of 93-97% for all testing sets. For voxel-level segmentation, the automated method achieved average values of 65-70% for DSC, 72-79% for PPV, 53-58% for IoU, and 62-73% for sensitivity in all testing sets. In the evaluation of volumetric parameters, there was a strong correlation between the manual and automated measurements of PSMA-TV and TL-PSMA for all centers.

CONCLUSIONS

The deep learning networks presented here offer promising solutions for automatically segmenting malignant lesions in prostate cancer patients using [68Ga]Ga-PSMA PET. These networks achieve a high level of accuracy in whole-body segmentation, as measured by the DSC and PPV at the voxel level. The resulting segmentations can be used for extraction of PET-derived quantitative biomarkers and utilized for treatment response assessment and radiomic studies.

An Update on the Role of mpMRI and 68Ga-PSMA PET Imaging in Primary and Recurrent Prostate Cancer

The objective of this work was to review comparisons of the efficacy of 68Ga-PSMA-11 (prostate-specific membrane antigen) PET/CT and multiparametric magnetic resonance imaging (mpMRI) in the detection of prostate cancer among patients undergoing initial staging prior to radical prostatectomy or experiencing recurrent prostate cancer, based on histopathological data. A comprehensive search was conducted in PubMed and Web of Science, and relevant articles were analyzed with various parameters, including year of publication, study design, patient count, age, PSA (prostate-specific antigen) value, Gleason score, standardized uptake value (SUVmax), detection rate, treatment history, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and PI-RADS (prostate imaging reporting and data system) scores. Only studies directly comparing PSMA-PET and mpMRI were considered, while those examining combined accuracy or focusing on either modality alone were excluded. In total, 24 studies comprising 1717 patients were analyzed, with the most common indication for screening being staging, followed by relapse. The findings indicated that 68Ga-PSMA-PET/CT effectively diagnosed prostate cancer in patients with suspected or confirmed disease, and both methods exhibited comparable efficacy in identifying lesion-specific information. However, notable heterogeneity was observed, highlighting the necessity for standardization of imaging and histopathology systems to mitigate inter-study variability. Future research should prioritize evaluating the combined diagnostic performance of both modalities to enhance sensitivity and reduce unnecessary biopsies. Overall, the utilization of PSMA-PET and mpMRI in combination holds substantial potential for significantly advancing the diagnosis and management of prostate cancer.

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.

68Ga-prostate specific membrane antigen-11 PET/CT versus multiparametric MRI in the detection of primary prostate cancer: A systematic review and head-to-head comparative meta-analysis

PURPOSE

The goal of this study was to evaluate the effectiveness of two diagnostic methods, 68Ga-PSMA-11 PET/CT and mpMRI, in detecting primary prostate cancer without limitations on the Gleason score.

METHODS

We conducted a comprehensive literature review, searching databases such as PubMed, Embase, and Web of Science until June 2023. Our objective was to identify studies that compared the efficacy of 68Ga-PSMA-11 PET/CT and mpMRI in detecting primary prostate cancer. To determine heterogeneity, the I2 statistic was used. Meta-regression analysis and leave-one-out sensitivity analysis were conducted to identify potential sources of heterogeneity.

RESULTS

Initially, 1286 publications were found, but after careful evaluation, only 16 studies involving 1227 patients were analyzed thoroughly. The results showed that the 68Ga-PSMA-11 PET/CT method had a pooled sensitivity and specificity of 0.87 (95 % CI: 0.80-0.92) and 0.80 (95 % CI: 0.69-0.89), respectively, for diagnosing prostatic cancer. Similarly, the values for mpMRI were determined as 0.84 (95 % CI: 0.75-0.92) and 0.74 (95 % CI: 0.61-0.86), respectively. There were no significant differences in diagnostic effectiveness observed when comparing two primary prostate cancer methodologies (pooled sensitivity P = 0.62, pooled specificity P = 0.50). Despite this, the funnel plots showed symmetry and the Egger test results (P values > 0.05) suggested there was no publication bias.

CONCLUSIONS

After an extensive meta-analysis, it was found that both 68Ga-PSMA-11 PET/CT and mpMRI demonstrate similar diagnostic effectiveness in detecting primary prostate cancer. Future larger prospective studies are warranted to investigate this issue further.

Applications of Artificial Intelligence in PSMA PET/CT for Prostate Cancer Imaging

Prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) has emerged as an important imaging technique for prostate cancer. The use of PSMA PET/CT is rapidly increasing, while the number of nuclear medicine physicians and radiologists to interpret these scans is limited. Additionally, there is variability in interpretation among readers. Artificial intelligence techniques, including traditional machine learning and deep learning algorithms, are being used to address these challenges and provide additional insights from the images. The aim of this scoping review was to summarize the available research on the development and applications of AI in PSMA PET/CT for prostate cancer imaging. A systematic literature search was performed in PubMed, Embase and Cinahl according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A total of 26 publications were included in the synthesis. The included studies focus on different aspects of artificial intelligence in PSMA PET/CT, including detection of primary tumor, local recurrence and metastatic lesions, lesion classification, tumor quantification and prediction/prognostication. Several studies show similar performances of artificial intelligence algorithms compared to human interpretation. Few artificial intelligence tools are approved for use in clinical practice. Major limitations include the lack of external validation and prospective design. Demonstrating the clinical impact and utility of artificial intelligence tools is crucial for their adoption in healthcare settings. To take the next step towards a clinically valuable artificial intelligence tool that provides quantitative data, independent validation studies are needed across institutions and equipment to ensure robustness.

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.

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.

Immunohistochemical and histopathological validation of 18 F-PSMA-1007 PET/CT for intraprostatic cancerous lesions

INTRODUCTION

Prostate-specific membrane antigen (PSMA) is overexpressed in prostate cancer (PCa). In this study, we aim to immunohistochemically and histopathological validate the fluorine-18 (18 F)-PSMA-1007 positron emission tomography/computed tomography (PET/CT) for intraprostatic PCa lesions.

METHODS

Between February 2019 and October 2020, patients with biopsy-proven, treatment-naïve intermediate-to-high-risk PCa undergoing an 18 F-PSMA-1007 PET/CT before robot-assisted radical prostatectomy (RARP) were prospectively enrolled. For all PCa lesions found on whole-mount histopathology, location, size, International Society of Urological Pathology (ISUP) grade group (GG), and immune reactive score (IRS) were assessed after PSMA staining. ISUP GG ≥ 3 PCa was defined as clinically significant (cs) PCa. All lesions were matched on PSMA PET/CT and the maximum standardized uptake value (SUVmax) was measured.

RESULTS

A total of 125 lesions were analyzed in the 80 RARP specimens, of which 49 (40%) were csPCa and 76 (60%) non-csPCa. Linear multivariable regressions showed that an increase in SUVmax significantly correlated with a higher ISUP GG (p values between 0.021 and 0.001) and a higher IRS (p = 0.017). Logistic multivariable regression showed that csPCa significantly correlated with a higher SUVmax (odds ratio, OR: 1.17 [95% confidence interval, CI: 1.04-1.21, p = 0.005]), an increase in tumor length (OR: 1.05 [95% CI 1.01-1.10, p = 0.020]) and a higher IRS (OR; 1.24 [95% CI 1.07-1.47, p = 0.006]). A SUVmax threshold of 4 would have resulted in one (2%) missed lesion with csPCa.

CONCLUSION

This prospective study revealed that 18 F-PSMA-1007 PET/CT SUVmax is correlated with the ISUP GG and IRS, and thereby could be a tool to characterize intraprostatic PCa lesions.

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.

Prognostic role of early prostate specific antigen changes after [177 Lu]Lu-PSMA radioligand therapy of metastasized prostate cancer: A meta-analysis

BACKGROUND

Approximately 10%-20% of prostate cancers progress to metastatic and castration-resistant forms (mCRPC). Radioligand (RLT) therapy with [177 Lu]Lu-prostate-specific membrane antigen (PSMA) is an emerging treatment for metastasized mCRPC and its efficacy is assessed not only but also by prostate specific antigen (PSA) measurement after 12 weeks or more after treatment. Our aim was to evaluate the role of early PSA measurement after RLT in predicting overall survival (OS) of mCRPC patients.

METHODS

A systematic search on PubMed, Web Of Science and Scopus was performed from January to December 2022. PRISMA guidelines for prognostic studies was adopted. Risk of bias was assessed using quality of prognostic studies (QUIPS).

RESULTS

Twelve studies at low-intermediate risk of bias, were included in the meta-analysis (1646 patients, mean age 70 years). About 50% of patients showed a PSA decline after 1-2 of [177 Lu]Lu-PSMA, and more than 30% reported a PSA decline ≥50%. The median OS range for patients with any PSA decline was 13-20 months, while for patients with stable or increased PSA, the median OS fell to 6-12 months. The OS rate for a PSA decline after the one-two [177 Lu]Lu-PSMA cycles was 0.39 (95% CI: 0.31-0.50), while OS for a PSA decline ≥50% was 0.69 (95% CI: 0.57-0.83).

CONCLUSIONS

A PSA decline is observed in almost 50% of mCRPC patients after 1-2 [177 Lu]Lu-PSMA cycles, with a significantly longer OS compared to stable or increased PSA levels, respectively. Accordingly, any PSA decline after 1-2 cycles of therapy should be regarded as a favourable prognostic factor for OS.

Population pharmacokinetic dosimetry model using imaging data to assess variability in pharmacokinetics of 177 Lu-PSMA-617 in prostate cancer patients

Studies to evaluate and optimize [177 Lu]Lu-PSMA treatment focus primarily on individual patient data. A population pharmacokinetic (PK) dosimetry model was developed to explore the potential of using imaging data as input for population PK models and to characterize variability in organ and tumor uptake of [177 Lu]Lu-PSMA-617 in patients with low volume metastatic prostate cancer. Simulations were performed to identify the effect of dose adjustments on absorbed doses in salivary glands and tumors. A six-compartment population PK model was developed, consisting of blood, salivary gland, kidneys, liver, tumor, and a lumped compartment representing other tissue (compartment 1-6, respectively), based on data from 10 patients who received [177 Lu]Lu-PSMA-617 (2 cycles, ~ 3 and ~ 6 GBq). Data consisted of radioactivity levels (decay corrected) in blood and tissues (9 blood samples and 5 single photon emission computed tomography/computed tomography scans). Observations in all compartments were adequately captured by individual model predictions. Uptake into salivary glands was saturable with an estimated maximum binding capacity (Bmax ) of 40.4 MBq (relative standard error 12.3%) with interindividual variability (IIV) of 59.3% (percent coefficient of variation [CV%]). IIV on other PK parameters was relatively minor. Tumor volume was included as a structural effect on the tumor uptake rate constant (k15 ), where a two-fold increase in tumor volume resulted in a 1.63-fold increase in k15 . In addition, interoccasion variability on k15 improved the model fit (43.5% [CV%]). Simulations showed a reduced absorbed dose per unit administered activity for salivary glands after increasing radioactivity dosing from 3 to 6 GBq (0.685 Gy/GBq vs. 0.421 Gy/GBq, respectively). All in all, population PK modeling could help to improve future radioligand therapy research.

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.

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.

Preliminary Findings of the Role of FAPi in Prostate Cancer Theranostics

Prostate cancer (PCa) is the most frequently diagnosed cancer worldwide and the second most common cause of cancer-related deaths among men. Progress in molecular imaging has magnified its clinical management; however, an unmet clinical need involves the identification of new imaging biomarkers that complement the gold standard of prostate-specific membrane antigen (PSMA) positron emission tomography (PET) in cases of clinically significant PCa that do not express PSMA. Fibroblast activation protein (FAP) is a type II transmembrane serine overexpressed in many solid cancers that can be imaged through quinoline-based PET tracers derived from an FAP inhibitor (FAPi). Preliminary results of FAPi application in PCa (in PSMA-negative lesions, and in comparison with fluorodeoxyglucose—FDG) are now available in the literature. FAP-targeting ligands for PCa are not limited to detection, but could also include therapeutic applications. In this preliminary review, we provide an overview of the clinical applications of FAPi ligands in PCa, summarising the main results and highlighting contemporary strengths and limitations.

Prostate-specific membrane antigen (PSMA) as a potential target for molecular imaging and treatment in bone and soft tissue sarcomas

Bone and soft tissue sarcomas are a group of rare malignant tumours with major histological and anatomical varieties. In a metastatic setting, sarcomas have a poor prognosis due to limited response rates to chemotherapy. Radioligand therapy targeting prostate-specific membrane antigen (PSMA) may offer a new perspective. PSMA is a type II transmembrane glycoprotein which is present in all prostatic tissue and overexpressed in prostate cancer. Despite the name, PSMA is not prostate-specific. PSMA expression is also found in a multitude of non-prostatic diseases including a subgroup of sarcomas, mostly in its neovascular endothelial cells. On PET/CT imaging, multiple sarcomas have also shown intense PSMA-tracer accumulation. PSMA expression and PSMA-tracer uptake seem to be highest in patients with aggressive and advanced sarcomas, who are also in highest need of new therapeutic options. Although these results provide a good rationale for the future use of PSMA-targeted radioligand therapy in a selection of sarcoma patients, more research is needed to gain insight into optimal patient selection methods, PSMA-targeting antibodies and tracers, administered doses of radioligand therapy, and their efficacy and tolerability. In this review, mRNA expression of the FOLH1 gene which encodes PSMA, PSMA immunohistochemistry, PSMA-targeted imaging and PSMA-targeted therapy in sarcomas will be discussed.

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.

The Role of [68Ga]PSMA PET/CT for Clinical Suspicion of Prostate Cancer in Patients with or without Previous Negative Biopsy: A Systematic Review

Simple Summary

In this paper we systematically evaluate the evidence regarding the role of [⁶⁸Ga]PSMA PET/CT for clinical suspicions of prostate cancer in patients with or without previous negative biopsy. A critical review of PubMed and Web of Science according to the PRISMA statement was conducted. Eighteen publications were selected for inclusion in the analysis. In 8 articles, there was a direct comparison with mpMRI. [⁶⁸Ga]PSMA PET/CT resulted more accurate in identifying primary prostate cancer with PSA values between 4 and 20 ng/mL than mpMRI. Moreover, its use combined with MRI improved sensitivity for csPCa detection, thus potentially avoiding unnecessary biopsies. Overall, [⁶⁸Ga]PSMA PET/CT resulted a promising technique in patients with clinical suspicion of PCa and precedent negative biopsy or contraindications to MRI.

Abstract

The purpose of the study is to systematically evaluate the evidence regarding the role of [⁶⁸Ga]PSMA PET/CT for clinical suspicions of prostate cancer in patients with or without previous negative biopsy. We performed a critical review of PubMed and Web of Science according to the PRISMA statement. Eighteen publications were selected for inclusion in this analysis. QUADAS-2 evaluation was adopted for quality analyses. [⁶⁸Ga]PSMA-11 was the radiotracer of choice in 15 studies, while [⁶⁸Ga]PSMA-617 was used in another 3. In 8 articles, there was a direct comparison with mpMRI. The total number of patients included was 1379, ranging from 15 to 291, with a median age of 64 years (range: 42–90). The median baseline PSA value was 12.9 ng/mL, ranging from 0.85 to 4156 ng/mL. Some studies evaluated the PSMA uptake comparing the SUVmax of suspicious lesions with the SUVmax of the normal biodistribution to find out optimal cut-off points. In addition, some studies suggested a significant association between PSA levels, PSA density, and [⁶⁸Ga]PSMA PET/CT finding. [⁶⁸Ga]PSMA PET/CT seems to be more accurate in identifying primary prostate cancer with PSA values between 4 and 20 ng/mL than mpMRI. Moreover, in some trials, the combination of PSMA PET/CT and MRI improved the NPV in the detection of clinically significant prostate cancer (csPCa) than MRI alone. Our findings are limited by the small numbers of studies and patient heterogeneity. [⁶⁸Ga]PSMA PET/CT is a promising technique in patients with clinical suspicion of PCa and precedent negative biopsy or contraindications to MRI. Furthermore, its use combined with MRI improves sensitivity for csPCa detection and can avoid unnecessary biopsies.

Prostate Cancer Biochemical Recurrence Resulted Negative on [68Ga]Ga-PSMA-11 but Positive on [18F]Fluoromethylcholine PET/CT

For prostate cancer (PCa) biochemical recurrence (BCR), the primarily suggested imaging technique by the European Association of Urology (EAU) guidelines is prostate-specific membrane antigen (PSMA) positron emission tomography/computer tomography (PET/CT). Indeed, the increased detection rate of PSMA PET/CT for early BCR has led to a fast and wide acceptance of this novel technology. However, PCa is a very heterogeneous disease, not always easily assessable with the highly specific PSMA PET with around 10% of cases occuring without PSMA expression. In this paper, we present the case of a patient with PCa BCR that resulted negative on [⁶⁸Ga]Ga-PSMA-11 PET/CT, but positive on [¹⁸F]Fluoromethylcholine (Choline) PET/CT.

Targeted prostate biopsy: 68Ga-PSMA PET/CT vs. mpMRI in the diagnosis of prostate cancer

Introduction: To evaluate the diagnostic accuracy of 68Ga-prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomog-raphy (PET/CT) vs. multiparametric magnetic resonance imag-ing (mpMRI) targeted biopsy (TPBx) in the diagnosis of clinical-ly significant prostate cancer (csPCa: Grade Group ≥ 2). Materials and methods: From January 2021 to June 2022, 100 patients (median age: 66 years) with negative digital rectal examination underwent transperineal prostate biopsy for abnor-mal PSA values (median 7.5 ng/ml). Before prostate biopsy, all patients underwent mpMRI and 68Ga-PET/CT examinations and mpMRI (PI-RADS version 2 ≥ 3) or 68Ga-PET/CT index lesions suspicious for cancer (SUVmax > 5 g/ml) underwent cognitive targeted cores (mpMRI-TPBx and PSMA-TPBx: four cores) com-bined with extended systematic prostate biopsy (eSPBx: median 18 cores). The procedure was performed transperineally using a tru-cut 18-gauge needle under sedation and antibiotic prophy-laxis. Results: PCa was found in 58/100 (58.0%) men; in detail, 44/58 (75.9%) were csPCa; mpMRI and 68Ga-PSMA showed 66/100 (66%) and 62/100 (60%) lesions suspicious for PCa, respective-ly. 68Ga-PSMA-TPBx vs. mpMRI-TPBx vs. eSPBx diagnosed 42 (95.4%) vs. 36 (81.8%) vs. 30 (68.2%) csPCa, respectively; mpMRI-TPBx vs. 68Ga-PSMA-TPBx showed a diagnostic accuracy of 76.9% vs. 84.9% in diagnosing csPCa. Conclusions: 68GaPSMA PET/CT TPBx demonstrated good accuracy in the diagnosis of csPCa, which was not inferior to mpMRI TPBx (84.9% vs. 76.9%) improving the detection rate for cancer of systematic biopsy.

Prostate specific membrane antigen positron emission tomography in primary prostate cancer diagnosis: First-line imaging is afoot

Prostate specific membrane antigen positron emission tomography (PSMA PET) is an excellent molecular imaging technique for prostate cancer. Currently, PSMA PET for patients with primary prostate cancer is supplementary to conventional imaging techniques, according to guidelines. This supplementary function of PSMA PET is due to a lack of systematic review of its strengths, limitations, and potential development direction. Thus, we review PSMA ligands, detection, T, N, and M staging, treatment management, and false results of PSMA PET in clinical studies. We also discuss the strengths and challenges of PSMA PET. PSMA PET can greatly increase the detection rate of prostate cancer and accuracy of T/N/M staging, which facilitates more appropriate treatment for primary prostate cancer. Lastly, we propose that PSMA PET could become the first-line imaging modality for primary prostate cancer, and we describe its potential expanded application.

Preclinical antibody-PET imaging of PD-L1

Programmed cell death protein-1/ligand-1 (PD-1/PD-L1) blockade, including antibody therapeutics, has transformed cancer treatment. However, a major challenge in the field relates to selecting patients who are likely to respond to immune checkpoint inhibitors. Indeed, biopsy-based diagnostic tests to determine immune checkpoint protein levels do not accurately capture the inherent spatial and temporal heterogeneity of PD-L1 tumor expression. As a result, not all PD-L1-positive tumors respond to immunotherapies, and some patients with PD-L1-negative tumors have shown clinical benefits. In 2018, a first-in-human study of the clinically-approved anti-PD-L1 antibody Atezolizumab labeled with the positron emitter zirconium-89 validated the ability of positron emission tomography (PET) to visualize PD-L1 expression in vivo and predict tumor response to immunotherapy. These studies have triggered the expansion of PD-L1-targeted immunoPET to assess PD-L1 protein levels and PD-L1 expression heterogeneity in real time and across the whole tumor. First, this mini-review introduces new PD-L1 PET imaging studies of the last 4 years, focusing on the expansion of preclinical tumor models and anti-PD-L1 antibodies/antibody fragments in development. Then, the review discusses how these preclinical models and targeting agents can be utilized to study spatial and temporal heterogeneity of PD-L1 expression.

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.

Could 68Ga-PSMA PET/CT Evaluation Reduce the Number of Scheduled Prostate Biopsies in Men Enrolled in Active Surveillance Protocols?

Background: To evaluate the accuracy of 68Ga-prostate specific membrane antigen (PSMA) PET/CT in the diagnosis of clinically significant prostate cancer (csPCa) (Grade Group > 2) in men enrolled in Active Surveillance (AS) protocol. Methods: From May 2013 to May 2021, 173 men with very low-risk PCa were enrolled in an AS protocol study. During the follow-up, 38/173 (22%) men were upgraded and 8/173 (4.6%) decided to leave the AS protocol. After four years from confirmatory biopsy (range: 48−52 months), 30/127 (23.6%) consecutive patients were submitted to mpMRI and 68Ga-PSMA PET/CT scan before scheduled repeated biopsy. All the mpMRI (PI-RADS > 3) and 68Ga-PET/TC standardised uptake value (SUVmax) > 5 g/mL index lesions underwent targeted cores (mpMRI-TPBx and PSMA-TPBx) combined with transperineal saturation prostate biopsy (SPBx: median 20 cores). Results: mpMRI and 68Ga-PSMA PET/CT showed 14/30 (46.6%) and 6/30 (20%) lesions suspicious for PCa. In 2/30 (6.6%) men, a csPCa was found; 68Ga-PSMA-TPBx vs. mpMRI-TPBx vs. SPBx diagnosed 1/2 (50%) vs. 1/2 (50%) vs. 2/2 (100%) csPCa, respectively. In detail, mpMRI and 68Ga-PSMA PET/TC demonstrated 13/30 (43.3%) vs. 5/30 (16.7%) false positive and 1 (50%) vs. 1 (50%) false negative results. Conclusion: 68Ga-PSMA PET/CT did not improve the detection for csPCa of SPBx but would have spared 24/30 (80%) scheduled biopsies showing a lower false positive rate in comparison with mpMRI (20% vs. 43.3%) and a negative predictive value of 85.7% vs. 57.1%, respectively.

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.

Quantitative imaging parameters to predict the local staging of prostate cancer in intermediate- to high-risk patients

Objectives

PSMA PET/MRI showed the potential to increase the sensitivity for extraprostatic disease (EPD) assessment over mpMRI; however, the interreader variability for EPD is still high. Therefore, we aimed to assess whether quantitative PSMA and mpMRI imaging parameters could yield a more robust EPD prediction.

Methods

We retrospectively evaluated PCa patients who underwent staging mpMRI and [68Ga]PSMA-PET, followed by radical prostatectomy at our institution between 01.02.2016 and 31.07.2019. Fifty-eight cases with PET/MRI and 15 cases with PET/CT were identified. EPD was determined on histopathology and correlated with quantitative PSMA and mpMRI parameters assessed by two readers: ADC (mm2/1000 s), longest capsular contact (LCC, mm), tumor volume (cm3), PSMA-SUVmax and volume-based parameters using a fixed threshold at SUV > 4 to delineate PSMAtotal (g/ml) and PSMAvol (cm3). The t test was used to compare means, Pearson’s test for categorical correlation, and ROC curve to determine the best cutoff. Interclass correlation (ICC) was performed for interreader agreement (95% CI).

Results

Seventy-three patients were included (64.5 ± 6.0 years; PSA 14.4 ± 17.1 ng/ml), and 31 had EPD (42.5%). From mpMRI, only LCC reached significance (p = 0.005), while both volume-based PET parameters PSMAtotal and PSMAvol were significantly associated with EPD (p = 0.008 and p = 0.004, respectively). On ROC analysis, LCC, PSMAtotal, and PSMAvol reached an AUC of 0.712 (p = 0.002), 0.709 (p = 0.002), and 0.718 (p = 0.002), respectively. ICC was moderate–good for LCC 0.727 (0.565–0.828) and excellent for PSMAtotal and PSMAvol with 0.944 (0.990–0.996) and 0.985 (0.976–0.991), respectively.

Conclusions

Quantitative PSMA parameters have a similar potential as mpMRI LCC to predict EPD of PCa, with a significantly higher interreader agreement.