Expression of PSMA in tumor neovasculature of high grade sarcomas including synovial sarcoma, rhabdomyosarcoma, undifferentiated sarcoma and MPNST

Incidental Finding of Spindle Cell Sarcoma on 68 Ga-PSMA-11 PET/CT

ABSTRACT

A 78-year-old man underwent 68 Ga-prostate-specific membrane antigen-11 (PSMA-11) PET/CT for biochemical recurrence of prostate adenocarcinoma following a simple prostatectomy. The scan showed PSMA-avid local recurrence within the prostatectomy bed and a suspicious right internal iliac nodal metastasis. In addition, there was a mildly avid subcutaneous lesion in the right flank, which revealed high-grade spindle cell sarcoma at histopathology. This case represents a potential pitfall for PSMA-11 PET imaging. The presentation of mildly avid, atypical soft tissue lesions should warrant a biopsy to allow for proper diagnosis and treatment management.

A Practical Guide to the Pearls and Pitfalls of PSMA PET Imaging

Prostate-specific membrane antigen (PSMA)-targeted PET agents have revolutionized the care of patients with prostate cancer, supplanting traditional methods of imaging prostate cancer, and improving the selection and delivery of therapies. This has led to a rapid expansion in both the number of PSMA PET scans performed and the imaging specialists required to interpret those scans. To aid those imagers and clinicians who are new to the interpretation of PSMA PET, this review provides an overview of the interpretation of PSMA PET/CT imaging and pearls for overcoming commonly encountered pitfalls. We discuss the physiologic distribution of the clinically available PSMA-targeted radiotracers, the commonly encountered patterns of prostate cancer spread, as well as the benign and malignant mimics of prostate cancer. Additionally, we review the standardized PSMA PET reporting systems and the role of PSMA in selecting appropriate patients for PSMA-targeted therapies.

Head-to-head comparisons of 68Ga-PSMA-11 and 18F-FDG PET/CT in evaluating patients with upper tract urothelial carcinoma: a prospective pilot study

PURPOSE

To prospectively compare the uptake of 68Ga-prostate specific membrane antigen (68Ga-PSMA)-11 and 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) in upper tract urothelial carcinoma (UTUC) and investigate the correlation between radiological parameters and pathological features of UTUC.

METHODS

Clinicopathologic and imaging data were collected from 10 UTUC patients who underwent preoperative 68Ga-PSMA-11 and 18F-FDG PET/CT scans. The diagnostic capabilities of both imaging techniques were analyzed and compared in UTUC. Angiogenesis in the malignancies was assessed using Chalkley counting and the expression of folate hydrolase 1 (FOLH1) and glucose transporter 1 (GLUT1) in UTUC were evaluated in the surgical specimens. Double immunofluorescence staining of PSMA and CD34 was used to examine tumor neovascularization. Tracer uptake and expression were compared and explored. Additionally, 10 patients with clear cell renal cell carcinoma (ccRCC) were included for prospective, comparative research.

RESULTS

Ten UTUC patients with 12 malignant lesions and another 10 ccRCC patients were included. 18F-FDG PET/CT demonstrated a more effective detection of UTUC foci compared to 68Ga-PSMA-11 PET/CT (the SUVmax of 18.48 ± 6.73 vs. 4.38 ± 1.45, P < 0.01). Immunohistochemical analysis revealed a statistically significant difference in the expression of PSMA and GLUT1 in UTUC (P = 0.048), with higher pathological grades showing more intense GLUT1 staining than PSMA (75% vs. 12.5%). The Chalkley counting of angiogenesis in ccRCC was significantly higher than that in UTUC (229.34 vs. 71.67), which was proportional to 68Ga-PSMA-11 PET/CT SUVmax (both P < 0.05).

CONCLUSION

18F-FDG PET/CT holds better clinical potential for evaluating UTUC and detecting lymph node metastasis compared to 68Ga-PSMA-11 PET/CT, likely due to the relatively scant expression of FOLH1 in tumor neovascular endothelium while the abundant expression of GLUT1 in malignancy. Furthermore, the lower neovascular density in UTUC should not be overlooked.

PSMA-targeted therapy for non-prostate cancers

Radioligand therapy (RLT) agents are demonstrating a crucial role in the clinical approach to aggressive malignancies such as metastatic castrate-resistant prostate cancer (m-CRPC). With the recent FDA approval of prostate-specific membrane antigen (PSMA)-targeted RLT for m-CRPC, the field has broadened its gaze to explore other cancers that express PSMA in the tumor parenchyma or tumor neovasculature. In this review article, we discuss current progress in the clinical use of PSMA RLTs in non-prostate cancers such salivary gland cancers, renal cell carcinoma, high grade glioma, and soft tissue sarcoma. We highlight early reports in small case series and clinical trials indicating promise for PSMA-targeted RLT and highlighting the importance of identifying patient cohorts who may most benefit from these interventions. Further study is indicated in non-prostate cancers investigating PSMA RLT dosimetry, PSMA PET/CT imaging as a biomarker, and assessing PSMA RLT safety and efficacy in these cancers.

68 Ga-PSMA-Avid Intranasal Solitary Fibrous Tumor

ABSTRACT

The utility of molecular imaging in solitary fibrous tumors has not been fully established. We present a rare case of recurrent intranasal solitary fibrous tumor incidentally localized on 68 Ga-PSMA PET/CT scan, which turned out to be metabolically inactive on 18 F-FDG PET/CT.

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.

PSMA Expression in Solid Tumors beyond the Prostate Gland: Ready for Theranostic Applications?

In the past decades, the expanding use of prostate-specific membrane antigen (PSMA) imaging for prostate cancer has led to the incidental detection of a lot of extra-prostatic malignancies showing an increased uptake of PSMA. Due to these incidental findings, the increasing amount of immunohistochemistry studies and the deeper knowledge of the mechanisms of expression of this antigen, it is now clear that “PSMA” is a misnomer, since it is not specific to the prostate gland. Nevertheless, this lack of specificity could represent an interesting opportunity to bring new insights on the biology of PSMA and its sites of expression to image and treat new conditions, particularly several cancers. In this review, we will describe the main extra-prostatic cancers that exhibit PSMA expression and that can be studied with PSMA-based positron emission tomography–computed tomography (PET/CT) as an additional or alternative tool to conventional imaging. In particular, we will focus on cancers in which a radioligand therapy with ¹⁷⁷lutetium has been attempted, aiming to provide an overview of the possible future theragnostic applications of PSMA.

Prostate-Specific Membrane Antigen Expression in Meningioma: A Promising Theranostic Target

Meningioma is the most common intracranial neoplasm, yet there is no effective therapy for recurrent/refractory meningiomas after surgery and radiation. Prostate-specific membrane antigen (PSMA) is an enzyme upregulated on endothelial cells of multiple neoplasms and is being investigated as a theranostic target. Until now, PSMA has not been studied in meningiomas. We aimed to verify PSMA endothelial expression in meningiomas, detect tumor grade variability, and investigate the relationship of PSMA signal with tumor recurrence. We analyzed 96 archival meningiomas including 58 de novo and 38 recurrent specimens. All specimens were stained routinely and immunostained for CD31 and PSMA. Slides were scanned and analyzed producing raw data for images of PSMA, CD31, PSMA/CD31, and PSMA/vasculature. PSMA expression was seen within 98.9% of meningioma samples. In the total cohort, higher-grade tumors had increased expression of raw PSMA and PSMA/CD31, and PSMA/vasculature ratios compared to grade 1 tumors. PSMA expression and PSMA/vasculature ratios (p = 0.0015) were higher in recurrent versus de novo tumors among paired samples. ROC curves demonstrated PSMA/CD31, PSMA/vasculature, and raw CD31 as indicators of tumor recurrence. Thus, PSMA is expressed within endothelial cells of meningiomas, is increased with tumor grade and recurrence, and persists with prior irradiation.

Expression of prostate-specific membrane antigen in the neovasculature of primary tumors and lymph node metastasis of laryngeal squamous cell carcinomas

Background

Prostate-specific membrane antigen (PSMA) expression is encountered in tumor-associated neovascularization.

Methods

PSMA-antibody was applied to the paraffin blocks of 51 patients who were diagnosed with squamous cell carcinoma of the larynx and underwent laryngectomy and one who underwent lymph node dissection. The percentage of vascular expression in tumoral and extratumoral stroma and lymph nodes and intensity score in tumoral epithelium were evaluated and divided into groups according to the level of PSMA expression. Final PSMA expression was determined by multiplying intensity and percentage scores.

Results

The mean age was 61±10 years. Patients with perineural invasion, cartilage invasion, and local invasion exhibited higher PSMA expression scores. Age, tumor differentiation, tumor diameter, perineural invasion, tumor localization, capsular invasion, depth of invasion, surgical margin status, local invasion, nodal metastasis, TNM classification, and stage were similar in high and low PSMA expression groups. There was no PSMA expression in extratumoral vascular stroma. Significantly higher PSMA expression was observed in the vascular endothelium of metastatic lymph nodes compared with reactive lymph nodes. Patients with advanced-stage disease exhibited higher PSMA vascular expression scores compared to those with earlier stages (p<.001). PSMA expression was not correlated with overall survival, disease-specific survival, or disease-free survival (p>.05).

Conclusions

Our study suggests that higher PSMA expression is associated with cartilage invasion, local invasion, and advanced-stage of disease. PSMA expression can be utilized for detection of lymph node metastasis and has some predictive role in cases of neck metastasis.

PSMA as a Theranostic Target in Hepatocellular Carcinoma: Immunohistochemistry and 68 Ga-PSMA-11 PET Using Cyclotron-Produced 68 Ga

Prostate-specific membrane antigen (PSMA) is a validated target for molecular diagnostics and targeted radionuclide therapy. Our purpose was to evaluate PSMA expression in hepatocellular carcinoma (HCC), cholangiocarcinoma (CCA), and hepatic adenoma (HCA); investigate the genetic pathways in HCC associated with PSMA expression; and evaluate HCC detection rate with 68 Ga-PSMA-11 positron emission tomography (PET). In phase 1, PSMA immunohistochemistry (IHC) on HCC (n = 148), CCA (n = 111), and HCA (n = 78) was scored. In a subset (n = 30), messenger RNA (mRNA) data from the Cancer Genome Atlas HCC RNA sequencing were correlated with PSMA expression. In phase 2, 68 Ga-PSMA-11 PET was prospectively performed in patients with treatment-naïve HCC on a digital PET scanner using cyclotron-produced 68 Ga. Uptake was graded qualitatively and semi-quantitatively using standard metrics. On IHC, PSMA expression was significantly higher in HCC compared with CCA and HCA (P < 0.0001); 91% of HCCs (n = 134) expressed PSMA, which principally localized to tumor-associated neovasculature. Higher tumor grade was associated with PSMA expression (P = 0.012) but there was no association with tumor size (P = 0.14), fibrosis (P = 0.35), cirrhosis (P = 0.74), hepatitis B virus (P = 0.31), or hepatitis C virus (P = 0.15). Overall survival tended to be longer in patients without versus with PSMA expression (median overall survival: 4.2 vs. 1.9 years; P = 0.273). FGF14 (fibroblast growth factor 14) mRNA expression correlated positively (rho = 0.70; P = 1.70 × 10-5 ) and MAD1L1 (Mitotic spindle assembly checkpoint protein MAD1) correlated negatively with PSMA expression (rho = -0.753; P = 1.58 × 10-6 ). Of the 190 patients who met the eligibility criteria, 31 patients with 39 HCC lesions completed PET; 64% (n = 25) lesions had pronounced 68 Ga-PSMA-11 standardized uptake value: SUVmax (median [range] 9.2 [4.9-28.4]), SUVmean 4.7 (2.4-12.7), and tumor-to-liver background ratio 2 (1.1-11). Conclusion: Ex vivo expression of PSMA in neovasculature of HCC translates to marked tumor avidity on 68 Ga-PSMA-11 PET, which suggests that PSMA has the potential as a theranostic target in patients with HCC.

Prostate-Specific Membrane Antigen in Anaplastic and Poorly Differentiated Thyroid Cancer-A New Diagnostic and Therapeutic Target?

Several studies have demonstrated an expression of the prostate-specific membrane antigen (PSMA) in the cancer-related neovasculature of thyroid malignancies. Due to the poor prognosis and limited therapeutic options for patients with anaplastic (ATC) and poorly differentiated (PDTC) thyroid carcinoma, the aim of our study was to investigate the theranostic approach of PSMA expression in these patients. The PSMA uptake on Gallium-68 (⁶⁸Ga)-PSMA-positron emission tomography/computed tomography (PET/CT) and glucose uptake on F-18-Fluordeoxyglucose (¹⁸F-FDG)-PET/CTs were analysed in two ATC and six PDTC patients. The PSMA expression in corresponding patients' tissue samples was detected by immunohistochemistry. In addition, various tissue sections from 22 ATC and six PDTC patients were examined concerning PSMA expression. ⁶⁸Ga-PSMA-PET/CT showed heterogeneous PSMA expression among patients and lesions. Six of the eight analyzed patients (two ATC, four PDTC) showed increased glucose metabolism without increased PSMA uptake after PET/CT. In one patient (PDTC), ¹⁸F-FDG-PET/CT tracer uptake was positive and ⁶⁸Ga-PSMA-PET/CT showed heterogeneous results. Another patient (PDTC) evidenced only PSMA-positive lesions and received two cycles of Lutetium-177 (¹⁷⁷Lu)-PSMA therapy, which kept his disease stable for seven months. There was a correlation between immunohistochemical PSMA expression and uptake on ⁶⁸Ga-PMSA-PET/CT in three of the examined patients. Twenty-seven of the analyzed 39 ATC and 13 of the analyzed 22 PDTC tissue sections showed a strong PSMA expression. Considering the rarity of PDTC and ATC, which is the reason for the small patient population we studied, the findings of this study confirm the high diagnostic sensitivity and superiority of ¹⁸F-FDG-PET/CT in comparison to ⁶⁸Ga-PSMA-PET/CT in the diagnosis of ATC and PDTC. However, it can be suggested that ⁶⁸Ga-PMSA-PET/CT can be considered as a beneficial adjunct to the well-established ¹⁸F-FDG-PET/CT for a few individual selected patients with ATC and PDTC to detect lesions not discovered by ¹⁸F-FDG-PET/CT and to determine patients' eligibility for a radioligand therapy. Radiolabelled PSMA-ligands may, in the future, represent a theranostic approach with only minor side effects for a few individual selected patients with ATC and PDTC who need alternative treatment options in case of progression when established therapies are no longer effective. However, due to the small sample size of our collective, larger studies are needed to allow for a final evaluation on the significance of PSMA-targeted diagnostic and therapy for ATC and PDTC.

Spotlight on PSMA as a new theranostic biomarker for bladder cancer

Bladder cancer (BCa) patients are diagnosed by cytology and cystoscopy. However, these diagnostic tests bear some limitations. We sought for reliable biomarkers to better determine BCa extension. Prostate-specific membrane antigen (PSMA) appears to fulfill this requirement in prostate cancer but its role in BCa has not been established yet. We then analyzed 87 bladder tissue samples from 74 patients assessing PSMA expression by immunohistochemistry. The median PSMA expression, exclusively found in tumor neovasculature, in terms of H-score significantly differed between non-tumor samples and tumor samples (p = 0.00288) showing a higher neovasculature-related PSMA expression. No differences were observed in relation to tumor type, grade and stage. BCa neovasculature-related PSMA overexpression may be useful in defining the degree of extension of the neoplasm. In addition, testing PSMA expression by immunohistochemistry may hold theranostic implications both considering anti-angiogenesis agents and radio-labelled PSMA ligands for intracavitary radionuclide therapy. In our opinion, BCa neovasculature-related PSMA overexpression may be considered an apt target for anti-angiogenesis and radionuclide treatment in BCa, once the evaluation of tumor-retention time for the appropriateness of long half-life therapeutic PSMA ligands as radionuclide treatment will be performed.

18F-PSMA-1007 PET/CT uptake in multiple angiolipomas caused by PSMA expression in capillaries: a case report

Prostate specific membrane antigen (PSMA) is a transmembrane glycoprotein that was originally cloned in the membrane of prostate gland epithelial cells. It has been confirmed to be highly expressed in prostate cancer cells, and in some non-prostatic tissues, including the brain and some benign lesions. PSMA-based imaging has been extensively used for the assessment of prostate carcinoma. The high uptake of PSMA imaging in these non-prostate cancer lesions may lead to some misdiagnosis. It is of important clinical significance to explore the possible causes of high PSMA uptake in these lesions. Here, we present a case of a 77-year-old man with prostate carcinoma who underwent a whole-body ¹⁸F-PSMA-1007 positron emission tomography/computed tomography (PET/CT) scan for staging. The results of the scan showed intense tracer uptake in both the prostatic bed and in multiple subcutaneous lesions. The subcutaneous lesions were later found to be angiolipomas by histopathological examination. Immunohistochemistry demonstrated strong positive cytoplasmic PSMA staining in lesional prostate cancer cells in prostate carcinoma, and mild-to-moderate positive cytoplasmic capillary PSMA staining in angiolipoma fatty density nodules. Our case report therefore demonstrated that ¹⁸F-PSMA-1007 PET/CT uptake in multiple angiolipomas was caused by PSMA expression in capillaries, and further knowledge of PSMA expression in benign lesions may be critical to minimize false-positive findings with ¹⁸F-PSMA-1007 PET/CT imaging.

Case of prostate stromal tumour of uncertain malignant potential where positron emission tomography with 18F-fluorodeoxyglucose was useful for surgical planning

Stromal tumour of uncertain malignant potential of the prostate is a rare tumour with a variable clinical behaviour ranging from incidentally detected indolent tumours that never progress, to aggressive diseases almost identical to sarcomas that may invade surrounding organs or develop metastases. Surgical excision is generally recommended for local diseases; however, owing to its diverse clinical outcomes, optimal management may vary from surgery alone to wide excision combined with chemotherapy and/or radiotherapy. Therefore, preoperative evaluation of the malignant potential of the disease is essential to decide the treatment strategy. Herein, we report a case of stromal tumour of uncertain malignant potential successfully treated with minimally invasive robot-assisted radical prostatectomy alone under the diagnosis of the disease with low malignant potential based on the findings of positron emission tomography with 18F-fluorodeoxyglucose.

Extrapleural solitary fibrous tumor evidenced by 68Ga-prostate-specific membrane antigen positron emission tomography/computed tomography study in the staging of a high-risk prostate cancer patient

Positron emission tomography/computed tomography (PET/CT) using ⁶⁸Ga-labeled prostate-specific membrane antigen (⁶⁸Ga-PSMA) became an important tool in the prostate cancer (PC) diagnosis. Despite its high sensitivity and specificity, this method may produce false-positive findings, as indicated by previous studies. This case report aims to warn nuclear medicine physicians, oncologists, and urologists about the possibility of false-positive findings using this imaging modality, especially in patients who have already been diagnosed with other malignancies. A 69-year-old man, previously treated for an extrapleural solitary fibrous tumor (ESFT), underwent staging tests after a new diagnosis of high-risk PC. ⁶⁸Ga-PSMA PET/CT imaging revealed an abnormal uptake in the prostate and in the right humerus. A biopsy was performed, and the pathology showed a lesion consisting of an ESFT metastasis. Diagnostic issues related to ⁶⁸Ga-PSMA PET/CT imaging should be disseminated to help physicians make appropriate treatment choices for each patient and avoid unnecessary procedures.

PSMA expression on neovasculature of solid tumors

The use of prostate specific membrane antigen (PSMA) binding agents, labelled with diagnostic and therapeutic radio-isotopes is opening the potential for a new era of personalized management of prostate carcinoma. A wide variety of immunohistochemistry studies have shown PSMA also to be upregulated on the endothelial cells of the neovasculature of a wide variety of other solid tumors where it may facilitate endothelial cell sprouting and invasion through its regulation of lytic proteases that have the ability to cleave the extracellular matrix. Similar to the introduction of PSMA-targeting theranostics in prostate carcinoma, overexpression of PSMA on newly formed tumor vessels may serve as a target for imaging and subsequent treatment of cancer through the use of agents that are capable of blocking PSMA in its function or through PSMA-mediated delivery of chemotherapeutics or radiation agents. In this review, the available data on PSMA expression on tumor neovasculature in human solid tumors assessed by using immunohistochemistry are discussed.

Optimization of PET protocol and interrater reliability of 18F-PSMA-11 imaging of prostate cancer

BACKGROUND

Several scan parameters for PET imaging with 18F-PSMA-11 such as dosage, acquisition time and scan duration were evaluated to determine the most appropriate scan protocol, as well as the effect of furosemide administration on lesion visualization. Forty-four patients were randomly assigned to a dosage group (2.0 ± 0.2 or 4.0 ± 0.4 MBq/kg 18F-PSMA-11). All patients received a full-body PET/CT 1 h and 3 h after radiotracer injection with a scan duration of 3 min/bed position. For comparison of the scan duration, images were reconstructed for 1.5 and 3 min/bed position. Patients were intravenously administered 0.5 mg/kg furosemide with a maximum dose of 40 mg. To evaluate the furosemide effect, 22 additional patients were recruited and received one full-body PET/CT 1 h after administration of 2.0 ± 0.2 MBq/kg 18F-PSMA-11 with a scan duration of 3 min/bed position. To this group, no furosemide was administered. Images were scored on image quality using a 7-point scale and each suspicious lesion was described. To assess interrater reliability, two nuclear physicians scored all scans independently and described all observed suspicious lesions.

RESULTS

The 4 MBq/kg group received for all reconstructed images (60 min p.i., 1.5 and 3 min/bed position and 180 min p.i., 1.5 and 3 min/bed position) the highest median image quality score compared to the 2 MBq/kg group (p values < 0.01). When comparing all reconstructed images, the highest image quality score was given to images at 60 min p.i., 3 min/bed position for both dosage groups (score 5 and 6 for 2 and 4 MBq/kg, respectively). The addition of furosemide administration decreased the interference score with one point (p = 0.01106) and facilitated the evaluation of lesions in proximity to the ureters. The interrater reliability for the comparison of each lesion separately after more than 40 18F-PSMA-11 scan readings showed an increasing κ value from 0.78 (95% CI, 0.65-0.92) to 0.94 (95% CI, 0.87-1).

CONCLUSION

Although the results indicate an administered activity of 4.0 ± 0.4 MBq/kg, preference will be given to 2.0 ± 0.2 MBq/kg due to the small difference in absolute score (max 1 point) and the ALARA principle. For evaluation of lesions in proximity to the ureters, the co-administration of a diuretic can be useful. The increase of the κ value from 0.78 to 0.94 suggests a learning curve in the interpretation of 18F-PSMA-11 images.

TRIAL REGISTRATION

Clinicaltrials.gov, NCT03573011. Retrospectively registered 28 June 2018.

Alpha-Particle Therapy for Multifocal Osteosarcoma: A Hypothesis

Osteosarcoma (OST) is the most common bone tumor in children and adolescents with a second peak of incidence in elderly adults usually diagnosed as secondary tumors in Paget's disease or irradiated bone. Subjects with metastatic disease or whose disease relapses after the initial therapy have a poor prognosis. Moreover, multifocal OST contains tumor-initiating cells that are resistant to chemotherapy. The use of aggressive therapies in an attempt to eradicate these cells can have long-term negative consequences in these vulnerable patient populations. ²²⁷Th-labeled molecular probes based on ligands to OST-associated receptors such as IGF-1R (insulin-like growth factor receptor 1), HER2 (human epidermal growth factor receptor 2), and PSMA (prostate-specific membrane antigen) are expected to detect and treat osseous and nonosseous sites of multifocal OST. Published reports indicate that ²²⁷Th has limited myelotoxicity, can be stably chelated to its carriers and, as it decays at targeted sites, ²²⁷Th produces ²²³Ra that is subsequently incorporated into the areas of increased osteoblastic activity, that is, osseous metastatic lesions. Linear energy transfer of α particles emitted by ²²⁷Th and its daughter ²²³Ra is within the range of the optimum relative biological effectiveness. The radiotoxicity of α particles is virtually independent of the phase in the cell cycle, oxygenation, and the dose rate. For these reasons, even resistant OST cells remain susceptible to killing by high-energy α particles, which can also kill adjacent quiescent OST cells or cells with low expression of targeted receptors. Systemic side effects are minimized by the limited range of these intense radiations. Quantitative single-photon emission computed tomography of ²²⁷Th and ²²³Ra is feasible. Additionally, the availability of radionuclide pairs, for example, ⁸⁹Zr for positron emission tomography and ²²⁷Th for therapy, establish a strong basis for the theranostic use of ²²⁷Th in the individualized treatment of multifocal OST.

The Added Value of Diagnostic and Theranostic PET Imaging for the Treatment of CNS Tumors

This review highlights the added value of PET imaging in Central Nervous System (CNS) tumors, which is a tool that has rapidly evolved from a merely diagnostic setting to multimodal molecular diagnostics and the guidance of targeted therapy. PET is the method of choice for studying target expression and target binding behind the assumedly intact blood-brain barrier. Today, a variety of diagnostic PET tracers can be used for the primary staging of CNS tumors and to determine the effect of therapy. Additionally, theranostic PET tracers are increasingly used in the context of pharmaceutical and radiopharmaceutical drug development and application. In this approach, a single targeted drug is used for PET diagnosis, upon the coupling of a PET radionuclide, as well as for targeted (nuclide) therapy. Theranostic PET tracers have the potential to serve as a non-invasive whole body navigator in the selection of the most effective drug candidates and their most optimal dose and administration route, together with the potential to serve as a predictive biomarker in the selection of patients who are most likely to benefit from treatment. PET imaging supports the transition from trial and error medicine to predictive, preventive, and personalized medicine, hopefully leading to improved quality of life for patients and more cost-effective care.

Looking for Drugs in All the Wrong Places: Use of GCPII Inhibitors Outside the Brain

In tribute to our friend and colleague Michael Robinson, we review his involvement in the identification, characterization and localization of the metallopeptidase glutamate carboxypeptidase II (GCPII), originally called NAALADase. While Mike was characterizing NAALADase in the brain, the protein was independently identified by other laboratories in human prostate where it was termed prostate specific membrane antigen (PSMA) and in the intestines where it was named Folate Hydrolase 1 (FOLH1). It was almost a decade to establish that NAALADase, PSMA, and FOLH1 are encoded by the same gene. The enzyme has emerged as a therapeutic target outside of the brain, with the most notable progress made in the treatment of prostate cancer and inflammatory bowel disease (IBD). PSMA-PET imaging with high affinity ligands is proving useful for the clinical diagnosis and staging of prostate cancer. A molecular radiotherapy based on similar ligands is in trials for metastatic castration-resistant prostate cancer. New PSMA inhibitor prodrugs that preferentially block kidney and salivary gland versus prostate tumor enzyme may improve the clinical safety of this radiotherapy. The wide clinical use of PSMA-PET imaging in prostate cancer has coincidentally led to clinical documentation of GCPII upregulation in a wide variety of tumors and inflammatory diseases, likely associated with angiogenesis. In IBD, expression of the FOLH1 gene that codes for GCPII is strongly upregulated, as is the enzymatic activity in diseased patient biopsies. In animal models of IBD, GCPII inhibitors show substantial efficacy, suggesting potential theranostic use of GCPII ligands for IBD.

Incidental Detection of a Radiation-Induced Soft-Tissue Sarcoma on 68Ga-PSMA PET/CT in a Patient Previously Treated for Prostate Cancer

Radiation-induced sarcoma is a rare complication of radiation therapy. We describe the incidental detection of a radiation-induced undifferentiated soft-tissue sarcoma with increased uptake on Ga-labeled prostate-specific membrane antigen (PSMA) PET/CT in a prostate cancer patient previously treated with surgery and external-beam radiotherapy. Results were confirmed by histological analysis. Ga-PSMA is known to bind not only to PSMA-expressing prostate cancer cells but also to the neovasculature of various other solid tumors. A careful Ga-PSMA PET/CT review of previously irradiated areas is warranted so as not to miss radiation-induced sarcoma in prostate cancer patients.

Neovascular PSMA expression is a common feature in malignant neoplasms of the thyroid

Aim

PSMA (prostate-specific membrane antigen) is physiologically expressed in normal prostate tissue and over expressed in prostate cancer cells, therefore constituting a potential target for antibody-based radioligand therapy. Very recent imaging findings reported PSMA-PET/CT uptake in various thyroid lesions. We were therefore encouraged to systematically analyse PSMA expression in different benign and malignant thyroid lesions.

Methods

Immunohistochemistry was used to detect PSMA expression in 101 thyroid lesions, while neovasculature was identified by CD34 immunostaining.

Results

PSMA expression in the neovasculature was significantly more frequent in malignant tumors (36/63; 57.1%) compared to benign diseases (5/38; 13.2%; p = 0.0001). In addition, PSMA expression levels in the neovasculature of poorly and undifferentiated thyroid cancers were significantly higher compared to differentiated thyroid tumors (p = 0.021). However, one case with a strong expression in follicular adenoma was identified.

Conclusions

We conclude that neovascular PSMA expression is common in thyroid cancer but may also rarely be found in benign thyroid diseases, such as follicular adenoma. High expression in the tumor-associated neovasculature is predominantly found in poorly differentiated and undifferentiated (anaplastic) thyroid cancer. This knowledge is highly relevant when interpreting PSMA/PET-CT scans from patients with prostate cancer. In addition, our findings might provide a rationale for further evaluation of PSMA-targeted anti-neovascular or radioligand therapy in metastatic dedifferentiated thyroid cancer.

Prostate specific membrane antigen (PSMA) expression in non-small cell lung cancer

OBJECTIVES

PSMA (prostate-specific membrane antigen) is overexpressed in prostate cancer cells and is reported to be a promising target for antibody-based radioligand therapy in patients with metastasized prostate cancer. Since PSMA expression is not restricted to prostate cancer, the underlying study investigates PSMA expression in non-small cell lung cancer (NSCLC).

MATERIAL AND METHODS

Immunohistochemistry was used to identify PSMA expression in n = 275 samples of NSCLC tissue specimens. By means of CD34 co-expression, the level of PSMA expression in tumor associated neovasculature was investigated. The impact of PSMA expression on clinicopathologic parameters and prognosis was evaluated.

RESULTS

PSMA tumor cell expression in NSCLC is as low as 6% and was predominantly found in squamous cell carcinoma (p = 0.002). Neovascular PSMA expression was found in 49% of NSCLC. High neovascular PSMA expression was associated with higher tumor grading (G3/G4) (p < 0.001). Neither for PSMA tumor cell expression, nor for PSMA neovascular cell expression prognostic effects were found for the investigated NSCLC cases.

CONCLUSION

Here, we report on the expression of PSMA in NSCLC tissue samples. Against the background of a potential treatment with radiolabeled PSMA ligands, our data might serve for the future identification of patients who could benefit from this therapeutic option.

Neovascular Prostate-Specific Membrane Antigen Expression Is Associated with Improved Overall Survival under Palliative Chemotherapy in Patients with Pancreatic Ductal Adenocarcinoma

Aims

Expression of PSMA (prostate-specific membrane antigen) has been demonstrated in various cancers, including pancreatic ductal adenocarcinoma (PDAC). However, PSMA expression in PDAC-associated neovasculature has so far not been systematically analyzed.

Methods and Results

We analyzed PSMA expression in 81 PDAC tissue samples from 61 patients. Microvessel density (MVD) was assessed by software-based image analysis and showed a mean MVD of 63.7 microvessels/0.785 mm². PSMA was practically absent in tumor tissue (5.3%) and PDAC cell lines (0/7) but could be detected in tumor-associated neovasculature in 53.2% of cases. There was no association between neovascular PSMA expression and clinicopathological tumor characteristics. Samples with PSMA+ neovasculature showed increased MVD; however, this result was not statistically significant (p > 0.05). Presence of PSMA+ neovessels correlated with overall survival under palliative chemotherapy (894 versus 400 days; HR 0.42; 95% CI: 0.12 to 0.87; p < 0.05).

Conclusion

PSMA expression in tumor-associated neovasculature is a common feature and associated with improved overall survival under palliative chemotherapy in PDAC. Our results point towards a possible association between PSMA expression and response to therapy which might be based on enhanced intratumoral bioavailability of systemic chemotherapy.

Prostate-specific membrane antigen PET imaging and immunohistochemistry in adenoid cystic carcinoma-a preliminary analysis

BACKGROUND

Adenoid cystic carcinoma (AdCC) of the head and neck is an uncommon malignant epithelial tumour of the secretory glands. Many patients develop slowly growing local recurrence and/or distant metastasis, for which treatment options are limited. A retrospective analysis of 9 AdCC patients was conducted to analyse the visualization of AdCC on PSMA PET/CT and to investigate the expression of PSMA on primary, recurrent and metastatic AdCC tumour tissue using immunohistochemistry.

RESULTS

Local recurrence occurred in six patients and eight developed distant metastasis. All PET/CTs depicted PSMA-ligand uptake. Four PSMA PET/CTs showed suspected residual disease, eight scans depicted uptake in areas suspected of distant metastasis. Median Maximum Standardized Uptake Value (SUVmax) in local recurrent and distant metastatic AdCC was 2.52 (IQR 2.41-5.95) and 4.01 (IQR 2.66-8.71), respectively. All primary tumours showed PSMA expression on immunohistochemistry (5-90% expression), as well as all available specimens of local recurrence and distant metastases.

CONCLUSION

PSMA PET/CT is able to detect and visualize local recurrent and distant metastatic AdCC. PSMA-specific targeting is supported by PSMA expression on immunohistochemistry.