Intense PSMA-expression using 68Ga-PSMA PET/CT in a paravertebral schwannoma mimicking prostate cancer metastasis

Prostate specific membrane antigen (PSMA) avid nonprostatic benign and malignant disease: a pictorial review

Prostate specific membrane antigen (PSMA) positron emission tomography-computed tomography (PET-CT) is revolutionising the management of prostate cancer (PC) in primary staging and assessment of biochemical recurrence (BCR) through its higher diagnostic accuracy compared to both conventional imaging and previously available PET radiopharmaceuticals. PSMA is a transmembrane glycoprotein, highly expressed in prostate cancer, with its extracellular domain the target for PSMA PET radiopharmaceuticals. However, PSMA expression is not prostate specific and resultant PSMA uptake on PET-CT is not restricted to pathologies arising from the prostate gland. The increasing use of PSMA PET-CT has revealed PSMA uptake in a variety of non-prostatic benign and malignant diseases, which adds complexity to PET-CT interpretation and subsequent clinical management. This pictorial review will provide a thorough knowledge and understanding of the comprehensive range of PSMA avid non-prostatic benign and malignant diseases demonstrable on PSMA PET-CT, whilst highlighting the complimentary nature of other imaging modalities.

Association of True Positivity with Serum Prostate-Specific Antigen Levels and Other Clinical Factors in Indeterminate PSMA-RADS-3A Lesions Identified on 18F-DCFPyL PET/CT Scans

The use of prostate-specific membrane antigen targeted PET imaging for the evaluation of prostate cancer has increased significantly in the last couple of decades. When evaluating these imaging findings based on the PSMA reporting and data system version 1.0, which categorize lesions based on their likelihood of prostate cancer involvement, PSMA-RADS-3A lesions are commonly seen, which are indeterminate for the presence of disease. A total of 28 patients with 171 PSMA-RADS-3A lesions on ¹⁸F-DCFPyL PET/CT scans from June 2016 to May 2017 who had follow-up cross-sectional imaging over time were included in this study. The PSA levels of patients with PSMA-RADS-3A lesions were categorized into four groups, 0-0.2, 0.2-1, 1-2, and >2 ng/mL. The pre-operative Gleason score of these patients was categorized into two groups, Gleason score < 7 or ≥7. The median age for these patients was 72.5 years (range 59-81). The median PSA value for patients with positive lesions was significantly higher than those with negative lesions (5.8 ng/mL vs. 0.2 ng/mL, p < 0.0001). The lesion positivity rate was significantly higher in patients with PSA > 1 ng/mL (18.2% vs. 81.9%, p < 0.001). On ROC analysis, the highest classification accuracy was seen at PSA ≥ 0.6 ng/mL of 80.12% (95% CI = 73.69-86.16%), and the area under the curve was 71.32% (95% CI = 61.9-80.7%, p < 0.0001). A total of 96.4% (108/112) of patients with positive lesions and 86.4% (51/59) of patients with negative lesions had a PSMA-RADS-4/5 lymph node on the initial ¹⁸F-DCFPyL PET/CT scan (p = 0.02). In patients with a Gleason score ≥ 7, the presence of positive PSMA-RADS-3A lesions was higher, compared to negative PSMA-RADS-3A lesions (p = 0.049). Higher PSA levels in patients with PSMA-RADS-3A lesions can point towards the presence of true positivity. PSA levels may be considered in deciding whether to call an indeterminate lesion on PSMA PET.

Incidental Detection of Radiotracer Uptake in Spindle Cell Lipoma on 18 F-PSMA PET/CT

ABSTRACT

An 84-year-old man underwent 18 F-prostate-specific membrane antigen (PSMA) PET/CT for staging of a newly diagnosed prostate adenocarcinoma. PET/CT revealed high 18 F-PSMA uptake in a thigh mass, which was initially suspected for a metastasis. Histopathology revealed a rare entity of spindle cell lipoma, which should be added to the reported list of neoplasms that can show "false-positive" PSMA uptake during evaluation of patients with prostate carcinoma representing a potential interpretative pitfall.

PSMA-Ligand Uptake in Disseminated Epidermoid Cysts in a PSMA PET/CT of a Patient With Recurrent Prostate Cancer

ABSTRACT

PSMA PET/CT is routinely used for the detection of prostate cancer (PC). However, increased PSMA-ligand uptake has been described in a variety of benign and malignant tissues. A 71-year-old man with biochemical recurrence of PC initially treated with radical prostatectomy was referred for PSMA-ligand PET/CT. Apart from 1 lymph node with intense PSMA-ligand uptake, suspicious for metastasis, disseminated PSMA-ligand-avid subcutaneous lesions were seen. Histopathology of 1 of these lesions revealed an epidermoid cyst. Physicians should remain cognizant of non-PC-related causes of increased PSMA-ligand uptake, of which this case represent yet another example.

A Critical Review of PET Tracers Used for Brain Tumor Imaging

The brain is a common site for metastases as well as primary tumors. Although evaluation of these malignancies with contrast-enhanced MR imaging defines current clinical practice, ¹⁸F-fluorodeoxyglucose (FDG)-PET has shown considerable utility in this area. In addition, many other tracers targeting various aspects of tumor biology have been developed and tested. This article discusses recent developments in PET imaging and the anticipated role of FDG and other tracers in the assessment of brain tumors.

Primary Peripheral Primitive Neuroectodermal Tumor of the Prostate on 18F-DCFPyL PET/CT

Peripheral primitive neuroectodermal tumor (PNET) is a group of malignant tumors composed of small round cells. Peripheral PNET usually originates in the skeletal system. However, the presence of PNET lesion in prostate is extremely rare. We report a case of a 40-year-old man who presented with dysuria for more than 2 months. Pelvic MRI indicated prostatic malignant tumor, and F-DCFPyL PET/CT showed an isolated prostatic mass with high uptake of F-DCFPyL. Although F-DCFPyL is very specific for prostatic adenocarcinoma, a final diagnosis of peripheral PNET was made by pathology examination.

Nonprostatic diseases on PSMA PET imaging: a spectrum of benign and malignant findings

PSMA PET imaging was originally used to assess biochemical recurrence of prostate cancer (PCa), but its clinical use was promptly extended to detection, staging and therapy response assessment. The expanding use of PSMA PET worldwide has also revealed PSMA ligand uptake in diverse nonprostatic diseases, which raised questions about the specificity of this imaging modality. Although not very common initially, a growing number of pathologies presenting PSMA uptake on PET have been reported in the last few years, and a proper interpretation of PSMA PET imaging findings suddenly became challenging and, to some extent, confusing. Compared to cytoplasmic PSMA expression in nonprostatic cells, the molecular features of apical PSMA expression in PCa cells can help to distinguish these various conditions. Correlations of imaging findings to patient history, to the expected pattern of disease spread and mainly to computed tomography (CT) and/or magnetic resonance imaging (MRI) characteristics will reinforce the distinction of lesions that are more likely related to PCa from those that could lead to an incorrect diagnosis. The overall benefits of endothelial PSMA expression, which is associated with the neovasculature of malignant neoplasms, will be highlighted, stating the potential use of PSMA ligand uptake as a theranostic tool. This review aims to cover the collection of nonprostatic diseases, including benign and malignant tumors, in a didactic approach according to disease etiology, with discussion of bone-related conditions and inflammatory and infectious processes.

Potential Causes of False-Negative Interpretations in 68Ga-PSMA PET/CT for the Detection of Local and Recurrent Prostate Cancer: An Underexposed Issue

Ga-PSMA PET/CT has emerged as a highly promising diagnostic method for the evaluation of prostate cancer. Although it is increasingly recognized that its specificity is imperfect, data on false-negatives in the prostate have been underreported. We present 3 cases with false-negatives for local (recurrent) prostate cancer on Ga-PSMA PET/CT, using multiparametric MRI and histopathology as reference standard. Metal artifact of prostate gold markers placed for external beam radiation therapy, low level of PSMA uptake, and bladder spillover are potential causes of misinterpretation. Awareness of these diagnostic pitfalls may improve Ga-PSMA PET/CT interpretation.

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.

Gallium-68 prostate-specific membrane antigen positron emission tomography/computed tomography compared with diagnostic computed tomography in relapsed prostate cancer

The aim of this study was to evaluate if prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) has a higher detection rate compared to standard contrast CT imaging for patients with a rising prostate-specific antigen (PSA) following definitive treatment (i.e., curative radical prostatectomy, radiotherapy, and brachytherapy) for prostate cancer in a private hospital setting. A retrospective single-site clinical audit was conducted on 150 PSMA PET/CT scans done for patients with a rising PSA after definitive treatment for prostate cancer. All studies were performed using I and T Ga-68 PSMA produced on a Scintomics radiopharmaceutical unit (Munich). All scans were performed on a GE 710 PET/CT scanner. All studies were compared to standard CT and other imaging. Of the 150 patients who had a ⁶⁸Gallium (Ga)-PSMA PET/CT for a rise in their PSA levels, 102/150 (68%) of patients had PSMA-avid scans compared to the conventional imaging group which had an overall detection rate of 42% (63/150). The rates of detection were 100%, 90%, 92%, 67%, and 25% at PSA levels of >10 μg/L, 5–10 μg/L, >1.5 μg/L, 0.5–1.5 μg/L, and <0.5 μg/L, respectively. PSMA PET/CT also solely picked up 39/102 (38%) of prostate cancer relapses compared to the conventional imaging group. In our study of 150 patients with biochemical recurrence of prostate cancer, ⁶⁸Ga-PSMA PET/CT demonstrated a superior detection rate (P < 0.05) compared to conventional imaging, including patients with low PSA levels (<0.5 μg/L).

An update on PET-based molecular imaging in neuro-oncology: challenges and implementation for a precision medicine approach in cancer care

PET imaging using novel radiotracers show promises for tumor grading and molecular characterization through visualizing molecular and functional properties of the tumors. Application of PET tracers in brain neoplasm depends on both type of the neoplasm and the research or clinical significance required to be addressed. In clinical neuro-oncology, ¹⁸F-FDG is used mainly to differentiate tumor recurrence from radiation-induced necrosis, and novel PET agents show attractive imaging properties. Novel PET tracers can offer biologic information not visible via contrast-enhanced MRI or ¹⁸F-FDG PET. This review aims to provide an update on the complementary role of PET imaging in neuro-oncology both in research and clinical settings along with presenting interesting cases in this context.

Recent Updates on Molecular Imaging Reporting and Data Systems (MI-RADS) for Theranostic Radiotracers-Navigating Pitfalls of SSTR- and PSMA-Targeted PET/CT

The theranostic concept represents a paradigmatic example of personalized treatment. It is based on the use of radiolabeled compounds which can be applied for both diagnostic molecular imaging and subsequent treatment, using different radionuclides for labelling. Clinically relevant examples include somatostatin receptor (SSTR)-targeted imaging and therapy for the treatment of neuroendocrine tumors (NET), as well as prostate-specific membrane antigen (PSMA)-targeted imaging and therapy for the treatment of prostate cancer (PC). As such, both classes of radiotracers can be used to triage patients for theranostic endoradiotherapy using positron emission tomography (PET). While interpreting PSMA- or SSTR-targeted PET/computed tomography scans, the reader has to navigate certain pitfalls, including (I.) varying normal biodistribution between different PSMA- and SSTR-targeting PET radiotracers, (II.) varying radiotracer uptake in numerous kinds of both benign and malignant lesions, and (III.) resulting false-positive and false-negative findings. Thus, two novel reporting and data system (RADS) classifications for PSMA- and SSTR-targeted PET imaging (PSMA- and SSTR-RADS) have been recently introduced under the umbrella term molecular imaging reporting and data systems (MI-RADS). Notably, PSMA- and SSTR-RADS are structured in a reciprocal fashion, i.e., if the reader is familiar with one system, the other system can readily be applied. Learning objectives of the present case-based review are as follows: (I.) the theranostic concept for the treatment of NET and PC will be briefly introduced, (II.) the most common pitfalls on PSMA- and SSTR-targeted PET/CT will be identified, (III.) the novel framework system for theranostic radiotracers (MI-RADS) will be explained, applied to complex clinical cases and recent studies in the field will be highlighted. Finally, current treatment strategies based on MI-RADS will be proposed, which will demonstrate how such a generalizable framework system truly paves the way for clinically meaningful molecular imaging-guided treatment of either PC or NET. Thus, beyond an introduction of MI-RADS, the present review aims to provide an update of recently published studies which have further validated the concept of structured reporting systems in the field of theranostics.

Gallium-68-Labeled Prostate-Specific Membrane Antigen-11 PET/CT of Prostate and Nonprostate Cancers

OBJECTIVE. The purpose of this study is to provide a concise summary of the current experience with ⁶⁸Ga-labeled prostate-specific membrane antigen (PSMA)-11 imaging of prostate and nonprostate malignancies and benign conditions. CONCLUSION. PSMA is overexpressed in prostate cancer and in the neovasculature of many other malignancies. The relevance of PSMA as a biologic target, coupled with advances in the design, synthesis, and evaluation of PSMA-based radionuclides for imaging and therapy, is anticipated to play a major role in patient care.

Prostate-specific membrane antigen positron emission tomography in the management of recurrent prostate cancer

INTRODUCTION

There is an unmet clinical need for early, accurate imaging of recurrent prostate cancer to improve patient outcomes. Staging, by conventional bone scintigraphy and CT have become outdated. 68Ga-PSMA PET/CT imaging in this setting has developed rapidly, with widespread International adoption in line with evidence-based guidelines in this group of patients.

SOURCES OF DATA

A PubMed search of English language articles was performed using following keywords: PSMA, PET/CT, biochemical recurrence, prostate cancer. The search revealed 85 articles, of which 75 were original; 70 of these involved use of the most widely available type of PSMA tracer (HBED). The review also relied on the clinical experience of reporting over 1000 PSMA PET/CT studies at a major tertiary referral centre for uro-oncology, with the majority of cases having been performed in the biochemical recurrence setting from 2015 to 2018.

AREAS OF AGREEMENT

68Ga-PSMA PET is a game changer and superior to choline PET and other established tracers which have been used in prostate cancer evaluation. Detection of recurrence at the prostate bed remains challenging due to bladder and urethral tracer accumulation. The main strength of PSMA PET/CT is its ability to identify small (<8 mm) pathological lymph nodes, upstaging nodal status in up to two-thirds of cases. Additionally, PSMA PET/CT, detects bone and bone marrow metastases missed by conventional bone and CT imaging. Thus, PSMA PET/CT has major impact on patient management, with studies reporting overall changes in 39-76% of cases.

AREAS OF CONTROVERSY

Controversy exists regarding patient access and NHS affordability of PSMA PET/CT imaging. Currently, no reimbursement is available under the NHS tariff system. The cost outlay for tertiary hospital linked PET centres ranges from £150-170 K. Large referral volumes, and technical advances in manufacturing process will make this tracer cost neutral and similar to the current funded, but less sensitive, choline PET. Current NICE guidelines for prostate cancer management do not include a recommendation on when PSMA PET/CT should be used and this is likely to remain the case in the next revision, due in 2019.

GROWING POINTS

Although PSMA PET/CT imaging results in significant management change, there is a need for high quality economic evaluation and cost analysis for this modality. Lack of this data will result in poor adoption of this technique and thus limit patient access. Furthermore, it is hoped that future tracers will become even more sensitive and identify disease at earlier thresholds.

AREAS TIMELY FOR DEVELOPING RESEARCH

Well-designed clinical trials with consideration of the health economic benefit of using PSMA PET/CT will be essential to provide a basis for entry into guidelines such as NICE and to provide a rationale for reimbursement.

68Ga-PSMA PET/CT in prostate cancer patients - patterns of disease, benign findings and pitfalls

Background

68Ga-PSMA PET/CT has an important role in assessment of prostate cancer patients with biochemical recurrence and is evolving in staging high- and intermediate risk disease. The aim of present study was to describe the metastatic patterns and frequency of involved sites of prostate cancer and to assess the incidence of benign Ga68-PSMA avid PET/CT findings in a large patient population.

Methods

68Ga-PSMA PET/CT studies performed in two tertiary medical centers over a period of 24 months were retrospectively reviewed. The incidence and location of pathological 68Ga-PSMA avid foci, suspicious to represent malignancy, as well as those of unexpected benign foci of increased 68Ga-PSMA activity were documented and analyzed.

Results

There were 445 68Ga-PSMA studies in 438 men (mean age 72.4, range 51–92 years) with prostate cancer referred for biochemical failure (n = 270, 61%), staging high-risk disease (n = 112, 25%), response assessment (n = 30, 7%), follow-up (n = 22, 5%) and suspected bone metastases (n = 11, 2%). 68Ga-PSMA avid disease sites were observed in 319 studies (72%), in 181 studies (67%) for biochemical recurrence, 94 studies for staging (84%) (p < 0.05), in 22 studies for response assessment (73%), 10 follow up studies (45%) and in five patients with suspected bone metastases (45%). 68Ga-PSMA avid lesions were most commonly detected in the prostate (n = 193, 43%), loco-regional spread (n = 51, 11%), abdomino-pelvic nodes (n = 129, 29%) and distant metastases (n = 158, 36%), including bone metastases (n = 11, 25%), distant lymphadenopathy (n = 29, 7%) and other organs (n = 18, 4%). Distant 68Ga-PSMA-avid metastases were commonly seen in patients with biochemical recurrence (14/21 lesions), but were not seen in patient referred for staging (p < 0.013). There were 96 non-malignant 68Ga-PSMA avid foci in 81 studies, most common in reactive lymph nodes (n = 36, 38%), nonmalignant bone lesions (n = 21, 22%), thyroid nodules (n = 9, 9%), ganglions (n = 9, 9%) and lung findings (n = 8, 8%).

Conclusion

The distribution of 68Ga-PSMA avid metastatic lesions is similar to data previously reported mainly from autopsy with comparable detection rates, indicating 68Ga-PSMA PET/CT is an accurate detection tool in patients with metastatic prostate cancer. If confirmed by further prospective studies 68Ga-PSMA PET/CT should be included in the guidelines to evaluate disease extent in these patients.

68Ga-PSMA Uptake in Angiolipoma

Ga-PSMA PET/CT is an imaging technique used in staging and detection of prostate cancer. However, enhanced uptake on Ga-PSMA PET/CT scan has also been ascribed to other malignant and benign lesions. We report on a case of a 56-year-old man with treated prostate carcinoma who had a Ga-PSMA PET/CT scan for restaging. Ga-PSMA uptakes in the prostatic bed and in multiple subcutaneous lesions were seen. Histopathology of a subcutaneous lesion revealed angiolipoma. It is important to be aware of the existence of the growing amount of reports on enhanced Ga-PSMA uptake unrelated to prostate cancer.

Molecular imaging reporting and data systems (MI-RADS): a generalizable framework for targeted radiotracers with theranostic implications

Both prostate-specific membrane antigen (PSMA)- and somatostatin receptor (SSTR)-targeted positron emission tomography (PET)-based imaging agents for prostate carcinoma and neuroendocrine tumors, respectively, are seeing rapidly expanding use. In addition to diagnostic applications, both classes of radiotracers can be used to triage patients for theranostic endoradiotherapy. While interpreting PSMA- or SSTR-targeted PET/computed tomography (CT) scans, the reader has to be aware of certain pitfalls. Adding to the complexity of the interpretation of those imaging agents, both normal biodistribution, and also false-positive and -negative findings differ between PSMA- and SSTR-targeted PET radiotracers. Herein summarized under the umbrella term molecular imaging reporting and data systems (MI-RADS), two novel RADS classifications for PSMA- and SSTR-targeted PET imaging are described (PSMA- and SSTR-RADS). Notably, PSMA- and SSTR-RADS are structured in a reciprocal fashion, i.e., if the reader is familiar with one system, the other system can readily be applied, as well. In the present review, we will discuss the most common pitfalls on PSMA- and SSTR-targeted PET/CT, briefly introduce PSMA- and SSTR-RADS, and define a potential future role of the umbrella framework MI-RADS compared to other classification systems.

Gastric Metastasis of Prostate Cancer as an Unusual Presentation Using 68Ga-Prostate-Specific Membrane Antigen PET/CT

A 79-year-old man with prostate cancer underwent Ga prostate-specific membrane antigen (Ga-PSMA) dual-time-point PET/CT scan to evaluate tumor activity due to early satiety, unquantified weight loss, and elevation of prostate-specific antigen (PSA), demonstrating thickening of the gastric wall with intense tracer uptake. The immunohistochemistry of gastric biopsy showed CDX2 and CK20: negative; CK7, focal positive; PSA, positive, which confirmed metastatic disease. Metastatic disease was also found in bones, right lung, and retroperitoneal and pelvic lymphadenopathies.

Prostate-Specific Membrane Antigen PET/CT Incidental Finding of a Schwannoma

We describe a case of a 73-year-old man with newly diagnosed prostate cancer referred to Ga-PSMA PET/CT for staging. A focal uptake of PSMA was visualized in the prostate compatible with primary prostate cancer. Outside the prostate, a PSMA-avid paravertebral soft tissue mass was observed. Further investigation with MRI of the same region showed signs compatible with schwannoma. This case shows the importance of including schwannoma in the differential diagnostic evaluation of patients with Ga-PSMA-positive foci in paravertebral locations, as schwannomas may show avid PSMA uptake and may potentially lead to an incorrect diagnosis of metastasis.

Uptake of the prostate-specific membrane antigen-targeted PET radiotracer 18F-DCFPyL in elastofibroma dorsi

OBJECTIVE

PET imaging using radiotracers that target prostate-specific membrane antigen (PSMA) are increasingly being used in the evaluation of men with prostate cancer (PCa). It is therefore of increasing importance for imaging specialists to recognize potential pitfalls of this novel imaging technique. In this report, we describe a series of benign elastofibroma dorsi with uptake of the PSMA-targeted PET radiotracer F-DCFPyL.

PATIENTS AND METHODS

We retrospectively analyzed the imaging data of 75 men with PCa who were consecutively imaged with F-DCFPyL PET/CT. Acquired images were reviewed for the presence of radiotracer uptake in the region of the scapular tip adjacent to the chest wall. Only those lesions with discrete radiotracer uptake corresponding to an area on CT with the characteristic appearance of an elastofibroma were considered positive.

RESULTS

In total, 18/75 (24.0%) patients had evidence of at least one elastofibroma dorsi on F-DCFPyL PET/CT. Eight (44.4%) of these patients had unilateral lesions, all of which were right sided. Detected lesions had a median maximal diameter of 2.3 cm (range: 1.3-8.4 cm) and a median perpendicular thickness to the chest wall of 0.9 cm (range: 0.6-2.5 cm). The median maximum standardized uptake value of detected lesions was 1.4 (range: 1.1-2.4) and the median maximum standardized uptake value corrected to lean body mass was 1.1 (range: 0.8-1.7).

CONCLUSION

This study is the first to report uptake of a PSMA-targeted PET radiotracer in elastofibroma dorsi. Radiotracer uptake in these benign lesions should not be falsely mistaken as sites of metastatic PCa.

68Ga-PSMA Uptake in Combined Hepatocellular Cholangiocarcinoma With Skeletal Metastases

Ga-PSMA PET is a rapidly evolving imaging modality for whole-body staging of prostate cancer. We report a case of a 70-year-old man with mildly elevated prostate-specific antigen (8.1 μg/L) and clinical suspicion of prostate cancer (osteoblastic metastases on radionuclide bone scan) who was referred for Ga-PSMA PET/CT for primary staging. Multiple Ga-PSMA-avid skeletal foci, mostly associated with lytic changes on low-dose CT, as well as hepatic foci of avid Ga-PSMA uptake, were identified. No abnormal focus of avid Ga-PSMA uptake was identified in the prostate. On histopathological examination, the liver lesion proved to be combined hepatocellular cholangiocarcinoma.

68Ga-PSMA-HBED-CC Uptake in Cervical, Celiac, and Sacral Ganglia as an Important Pitfall in Prostate Cancer PET Imaging

The study aims to investigate the presence of physiologic prostate-specific membrane antigen (⁶⁸Ga-PSMA)-ligand uptake on PET in cervical, celiac, and sacral ganglia of the sympathetic trunk as a pitfall for lymph node metastases in prostate cancer imaging. Methods: Four hundred seven patients who underwent Glu-NH-CO-NH-Lys radiolabeled with ⁶⁸Ga-gallium N,N-bis[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-N,N-diacetic acid (⁶⁸Ga-PSMA-HBED-CC) PET (combined with a diagnostic CT) were retrospectively analyzed. The number of ⁶⁸Ga-PSMA PET-positive cervical, celiac, and sacral ganglia was determined, and the configuration and SUV_max of each ganglion were measured. In addition, the configuration and SUV_max of adjacent lymph node metastases in the respective region (cervical, celiac, or sacral) were determined. Results:⁶⁸Ga-PSMA-ligand uptake above background was detected in 401 (98.5%) patients in any peripheral ganglia, in 369 (92%) patients in cervical ganglia, in 363 (89%) patients in celiac ganglia, and in 183 (46%) patients in sacral ganglia. The ⁶⁸Ga-PSMA-ligand uptake was highest in celiac (mean SUV_max, 2.9 ± 0.8 vs. cervical mean SUV_max, 2.4 ± 0.6) and sacral (mean SUV_max 1.7 ± 0.5; both P < 0.0001) ganglia. Intraindividually there was a statistically significant but weak to moderate correlation between the ⁶⁸Ga-PSMA-ligand uptake in cervical versus celiac ganglia (R = 0.34, P < 0.0001), cervical versus sacral (R = 0.52, P < 0.0001), and celiac versus sacral (R = 0.16, P < 0.05). The ⁶⁸Ga-PSMA-ligand uptake was significantly more intense in adjacent lymph node metastases than the respective ganglia (cervical: 18.0 ± 16.2 vs. 2.4 ± 0.6, P < 0.0001; celiac: 13.5 ± 12.3 vs. 2.9 ± 0.8, P < 0.0001; sacral: 13.4 ± 11.6 vs. 1.7 ± 0.5, P < 0.0001). Furthermore, ganglia predominantly exhibit a band-shaped configuration (71.2%), followed by a teardrop (26.8%) and only rarely a nodular configuration (2.0%). Conversely, lymph node metastases are only rarely band-shaped (1.1%), but more often show teardrop (40.3%) or nodular appearance (58.6%) (P < 0.00001). Conclusion:⁶⁸Ga-PSMA-ligand uptake in ganglia along the sympathetic trunk as assessed by ⁶⁸Ga-PSMA-HBED-CC PET represents an important pitfall in prostate cancer PET imaging. The ⁶⁸Ga-PSMA-ligand uptake is higher in celiac ganglia than cervical or sacral ganglia, and the level of ⁶⁸Ga-PSMA-ligand uptake seems to be patient-related. For the differentiation between lymph node metastases and sympathetic ganglia, both intensity of ⁶⁸Ga-PSMA-ligand uptake and exact localization and configuration of the respective lesion should be examined carefully.

Mesenchymal tumors of the prostate

Mesenchymal tumors of the prostate are rare but often cause considerable diagnostic difficulty when encountered. These may be either benign or malignant and can arise within the prostate gland or in adjacent tissues. This review covers prostatic stromal proliferations (prostatic stromal tumor of uncertain malignant potential and stromal sarcoma), solitary fibrous tumor, myofibroblastic proliferations, smooth muscle neoplasms (leiomyoma and leiomyosarcoma), gastrointestinal stromal tumor, schwannoma, rhabdomyosarcoma, sarcomatoid carcinoma, postradiation sarcoma, and mixed epithelial stromal tumor of the seminal vesicle. Differential diagnostic considerations are emphasized, including descriptions of helpful histological and/or clinical clues and the use of adjuvant diagnostic techniques.

Performance of 68Ga-PSMA PET/CT for Prostate Cancer Management at Initial Staging and Time of Biochemical Recurrence

PURPOSE OF THE REVIEW

Recently introduced Gallium-68 labeled PSMA-ligands such as HBED-CC (⁶⁸Ga-PSMA) have shown promise for unmet diagnostic needs in prostate cancer.

RECENT FINDINGS

⁶⁸Ga-PSMA has demonstrated improved detection rates and specificity for prostate cancer compared to standard imaging approaches. In the setting of primary disease, ⁶⁸Ga-PSMA appears to preferentially identify treatment-relevant intermediate and high-risk prostate cancer. There is also a growing evidence that ⁶⁸Ga-PSMA positron emission tomography (PET) outperforms alternative conventional imaging methods including choline-based radiotracers for the localization of disease sites at biochemical recurrence, particularly at lower prostate-specific antigen (PSA) levels (< 1 ng/mL). However, the majority of published work lacks rigorous verification of imaging results. ⁶⁸Ga-PSMA offers significant promise for both, primary disease and biochemically recurrent prostate cancer. The evidence base to support ⁶⁸Ga-PSMA is however still underdeveloped, and more rigorous studies substantiating efficacy are needed.

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.

Pearls and pitfalls in clinical interpretation of prostate-specific membrane antigen (PSMA)-targeted PET imaging

BACKGROUND

The rapidly expanding clinical adaptation of prostate-specific membrane antigen (PSMA)-targeted PET imaging in the evaluation of patients with prostate cancer has placed an increasing onus on understanding both the potential pearls of interpretation as well as limitations of this new technique. As with any new molecular imaging modality, accurate characterization of abnormalities on PSMA-targeted PET imaging can be accomplished only if one is aware of the normal distribution pattern, physiological variants of radiotracer uptake, and potential sources of false-positive and false-negative imaging findings. In recent years, a growing number of reports have come to light describing incidental non-prostatic benign or malignant pathologies with high uptake on PSMA-targeted PET imaging. In this review, we have summarized the published literature regarding the potential pearls and technical and interpretive pitfalls of this imaging modality. Knowledge of these limitations can increase the confidence of interpreting physicians and thus improve patient care.

CONCLUSIONS

As PSMA-targeted PET is expected to be evaluated in larger prospective trials, the dissemination of potential diagnostic pitfalls and the biologic underpinning of those findings will be of increased importance.

PSMA Ligands for PET Imaging of Prostate Cancer

Targeting the prostate-specific membrane antigen (PSMA) with ⁶⁸Ga-labeled and ¹⁸F-labeled PET agents has become increasingly important in recent years. Imaging of biochemically recurrent prostate cancer has been established as a widely accepted clinical indication for PSMA ligand PET/CT in many parts of the world because of the results of multiple, primarily retrospective, studies that indicate superior detection efficacy compared with standard-of-care imaging. For high-risk primary prostate cancer, evidence is growing that this modality significantly aids in the detection of otherwise occult nodal and bone metastases. For both clinical indications in recurrent as well as in primary prostate cancer, preliminary data demonstrate a substantial impact on clinical management. Emerging data imply that intraprostatic tumor localization, therapy stratification, and treatment monitoring of advanced disease in specific clinical situations might become future indications. Current criteria for image reporting of PSMA ligand PET are evolving given the expanding body of literature on physiologic and pathologic uptake patterns and pitfalls. This article intends to give an educational overview on the current status of PSMA ligand PET imaging, including imaging procedure and interpretation, clinical indications, diagnostic potential, and impact on treatment planning.

68Ga-PSMA-11 PET/CT: the rising star of nuclear medicine in prostate cancer imaging?

Ever since the introduction of ⁶⁸Ga-prostate-specific membrane antigen 11 positron-emission tomography/computed tomography (⁶⁸Ga-PSMA-11 PET/CT) a few years ago, it has rapidly achieved great success in the field of prostate cancer imaging. A large number of studies have been published to date, indicating a high potential of ⁶⁸Ga-PSMA-11 PET/CT in the work-up of prostate cancer patients, including primary diagnosis, staging and biochemical recurrence. The aim of this review is to present the most important data on this novel, highly promising imaging technique, and to formulate recommendations for possible applications of ⁶⁸Ga-PSMA-11 PET/CT in clinical routine.

PSMA Uptake in Mediastinal Sarcoidosis

Prostate-specific membrane antigen (PSMA) is a cell surface glycoprotein which is frequently overexpressed on prostate cancer cells. Ga-PSMA PET/CT plays an increasing role in prostate cancer management. However, growing evidence suggests increased PSMA uptake in a variety of other malignant tumor entities and in some benign lesions. This report describes PSMA uptake in numerous thoracic lymph nodes in a patient with known mediastinal sarcoidosis. Knowledge and recognition of these possibilities are important to avoid scan misinterpretation.

Diagnostic performance of 68Ga-PSMA-11 (HBED-CC) PET/CT in patients with recurrent prostate cancer: evaluation in 1007 patients

Purpose

Since the clinical introduction of ⁶⁸Ga-PSMA-11 PET/CT, this imaging method has rapidly spread and is now regarded as a significant step forward in the diagnosis of recurrent prostate cancer (PCa). The aim of this study was to analyse the influence of several variables with possible influence on PSMA ligand uptake in a large cohort.

Methods

We performed a retrospective analysis of 1007 consecutive patients who were scanned with ⁶⁸Ga-PSMA-11 PET/CT (1 h after injection) from January 2014 to January 2017 to detect recurrent disease. Patients with untreated primary PCa or patients referred for PSMA radioligand therapy were excluded. The possible effects of different variables including PSA level and PSA doubling time (PSA_DT), PSA velocity (PSA_Vel), Gleason score (GSC, including separate analysis of GSC 7a and 7b), ongoing androgen deprivation therapy (ADT), patient age and amount of injected activity were evaluated.

Results

In 79.5% of patients at least one lesion with characteristics suggestive of recurrent PCa was detected. A pathological (positive) PET/CT scan was associated with PSA level and ADT. GSC, amount of injected activity, patient age, PSA_DT and PSA_Vel were not associated with a positive PET/CT scan in multivariate analysis.

Conclusion

⁶⁸Ga-PSMA-11 PET/CT detects tumour lesions in a high percentage of patients with recurrent PCa. Tumour detection is clearly associated with PSA level and ADT. Only a tendency for an association without statistical significance was found between higher GSC and a higher probability of a pathological PET/CT scan. No associations were found between a pathological ⁶⁸Ga-PSMA-11 PET/CT scan and patient age, amount of injected activity, PSA_DT or PSA_Vel.

Electronic supplementary material

The online version of this article (doi:10.1007/s00259-017-3711-7) contains supplementary material, which is available to authorized users.

Gallium-68 Prostate-Specific Membrane Antigen PET Imaging

The role of gallium-68 (⁶⁸Ga) prostate-specific membrane antigen (PSMA) PET imaging is evolving and finding its place in the imaging armamentarium for prostate cancer (PCa). Despite the progress of conventional imaging strategies, significant limitations remain, including identification of small-volume disease and assessment of bone. Clinical studies have demonstrated that ⁶⁸Ga-PSMA is a promising tracer for detection of PCa metastases, even in patients with low prostate-specific antigen. To provide an accurate interpretation of ⁶⁸Ga-PSMA PET/computed tomography, nuclear medicine specialists and radiologists should be familiar with physiologic ⁶⁸Ga-PSMA uptake, common variants, patterns of locoregional and distant spread of PCa, and inherent pitfalls.

68Ga-PSMA Uptake in Hepatocellular Carcinoma

Ga-PSMA based integrated PET/MRI is emerging as a novel imaging technique for the staging of prostate carcinoma. We report a case of a 77-year-old man with raised prostate-specific antigen who presented to us for Glu-NH-CO-NH-Lys-(Ahx)-[Ga-(HBED-CC)] (Ga-PSMA) simultaneous PET/MRI scan for prostate cancer evaluation. A PSMA avid hepatic lesion on the background of cirrhotic liver was noted apart from PSMA avid lesion in the peripheral gland of the prostate. On histopathological examination, the hepatic lesion turned out to be hepatocellular carcinoma.

Incidental Meningioma Mimicking Metastasis of Prostate Adenocarcinoma in 68Ga-Labeled PSMA Ligand PET/CT

A 67-year-old man with prostate adenocarcinoma underwent Ga-labeled prostate-specific membrane antigen (PSMA) ligand PET/CT for restaging due to a rising prostate-specific antigen level. Local recurrence in the prostatic region and a metastasis in the left iliac bone were detected showing high PSMA expression. A mass lesion was seen in the left orbitofrontal region with high Ga PSMA uptake. The successive MRI confirmed that the lesion was consistent with meningioma.

PSMA Expression in Multinodular Thyroid Neoplasm on Simultaneous Ga-68-PSMA PET/MRI

PSMA PET is increasingly being used in imaging of recurrent prostate carcinoma. A case with suspected recurrent Prostate carcinoma (PCa), raised PSA (Prostate specific antigen) and suspected spinal metastases was referred for whole body Ga-68-PSMA PET/MRI.

The study revealed PSMA avid recurrent prostate mass and extensive osseous metastases. Abnormal PSMA uptake in the thyroid gland prompted USG-guided FNAC which revealed Hurthle cell neoplasm. Histopathological examination (HPE) of excised gland showed multiple Hurthle cell adenomas in both lobes of thyroid along with foci of papillary thyroid carcinoma which on immunohistochemistry were thyroglobulin positive and PSA negative.

Rare Paravertebral and Skull Base Metastases in Prostate Cancer

Prostate cancer is the most commonly diagnosed visceral cancer in the United States. A majority of cases exhibit an insidious course and nonaggressive tumor behavior. Prostate cancer can manifest as lesions which remain localized, regionally invading or metastasize to lymph nodes, bones, and lungs. Here, we report a unique case of metastatic prostate cancer to the right upper mediastinum, presenting as a paravertebral mass within 2 years of initial tissue diagnosis. Paravertebral spread has not been described for prostate cancer, and herein, we discuss the clinical presentation, diagnostic workup, and possible therapeutic options available in light of the literature.