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

Comparison of 68Ga-PSMA-HBED-CC and 18F-FDG PET/CT in the Evaluation of Adenoid Cystic Carcinoma-A Prospective Study

PURPOSE OF STUDY

18F-FDG PET/CT plays a major role in diagnosis and staging of head and neck cancer; however, FDG has lower uptake in adenoid cystic carcinoma (AdCC). Prostate-specific membrane antigen (PSMA) expression is found to be associated with endothelial cells or tumor neovasculature in malignant AdCC and salivary duct carcinoma. Thus, present study is aimed to compare the role of 68Ga-PSMA and 18F-FDG PET/CT in patients with primary and/or metastatic AdCC.

MATERIALS AND METHODS

Histopathologically proven AdCC patients were intravenously injected with 370 MBq (10 mCi) of 18F-FDG and 111-185 MBq (3-5 mCi) of 68Ga-PSMA. Images were acquired at 60 and 45 minutes postinjection for 18F-FDG and 68Ga-PSMA, respectively, on dedicated PET/CT scanners. Visual and semiquantitative analyses of PSMA expression in regional and metastatic sites were performed by 2 experienced nuclear medicine physicians.

RESULTS

Seventeen patients (7 men, 10 women) having mean age of 44 ± 14.19 years were prospectively included in the study. Of 17 patients, FDG PET/CT was performed in only 14 (82%) patients. PSMA and FDG uptakes were seen at the primary site in 16 (94%) and 13 (93%) patients, respectively, whereas 1 patient was postradical tumor excision. Lung lesions (n = 7) and lymph nodes (n = 5) were detected on both FDG and PSMA PET scans. However, cerebellar and meningeal metastasis (n = 1, 6%) and bony lesions (n = 2, 12%) were detected only on PSMA PET/CT but not visualized on FDG PET/CT scan.

CONCLUSIONS

PSMA may have theranostic importance in unresectable or metastatic AdCC, besides having a role in staging/restaging.

PSMA-Directed Imaging and Therapy of Salivary Gland Tumors: A Single-Center Retrospective Study

We analyzed the diagnostic performance of prostate-specific membrane antigen (PSMA) PET/CT and the dosimetry, efficacy, and safety of 177Lu-PSMA-617 radioligand therapy (RLT) in salivary gland malignancies (SGMs). Methods: We identified 28 SGM patients with PSMA PET/CT from our database. CT and PSMA PET/CT images were evaluated separately by 3 masked readers in joint reading sessions. Pathologic findings were grouped into 6 TNM regions, and lesion-based disease extent was classified as no disease (n = 1, 4%), unifocal (n = 2, 7%), oligometastatic (n = 9, 32%), multifocal (n = 3, 11%), or disseminated (n = 13, 47%). For each region, the SUVmax of the lesion with the highest uptake was measured and the visual PSMA expression score was evaluated on a per-patient basis using PROMISE criteria. The association between PSMA expression and clinical and histopathologic markers was tested using the Student t test. Five patients underwent PSMA RLT with intratherapeutic dosimetry. Response was assessed using RECIST 1.1, and adverse events were graded according to version 5.0 of the Common Terminology Criteria for Adverse Events. Results: Compared with CT, PSMA PET/CT demonstrated additional metastatic lesions in 11 of 28 (39%) patients, leading to upstaging of TNM and lesion-based disease extent in 3 (11%) and 6 (21%) patients, respectively. PSMA PET/CT detected CT-occult local tumor, regional lymph nodes, nonregional lymph nodes, and bone metastases in 1 (4%), 4 (14%), 2 (7%), and 4 (14%) patients, respectively; no additional lesions were detected in the other predefined regions. PSMA expression level was higher than liver in 6 patients (25%). A significantly higher SUVmax was observed in male than female patients (15.8 vs. 8.5, P = 0.007) and in bone than lung lesions (14.2 vs. 6.4, P = 0.006). PSMA RLT was discontinued after 1 cycle in 3 of 5 patients because of insufficient tumor doses. No adverse events of grade 4 or higher occurred. Conclusion: In SGMs, PSMA PET/CT demonstrated a superior detection rate and led to upstaging in about one third of patients when compared with CT. The male sex and the presence of bone metastases were associated with significantly higher PSMA expression. PSMA RLT was well tolerated, but most patients did not have more than 1 cycle because of insufficient tumor doses.

Histological Validation of FDG and PSMA-Targeted PET/CT Imaging in a Rare Tracheal Adenoid Cystic Carcinoma

ABSTRACT

Adenoid cystic carcinomas are the second most common entity of tracheal malignancies, which have an overall incidence as low as only 0.2 in 100,000 persons per year. We present the case of a 64-year-old man with a histologically confirmed adenoid cystic carcinoma who sequentially underwent 18F-FDG PET/CT and 68Ga-PSMA-11 PET/CT within 1 day for staging 3 days before surgical resection of the tumor. Immunohistochemistry revealed PSMA expression of the tumor corroborating the PSMA PET findings.

The Importance of Prostate-Specific Membrane Antigen Expression in Salivary Gland Tumors

Objective

Prostate-specific membrane antigen (PSMA) is a cell membrane protein expressed by prostate tissues. It is not prostate specific and is also expressed by some non-prostatic solid neoplasms. Our study aimed to investigate the potential role of PSMA in salivary gland tumors.

Methods

The present study was designed to retrospectively analyze our cases that presented with salivary gland tumors. The files of 105 patients were reviewed and their paraffin embedded blocks were retrieved from the pathology department. Immunohistochemical examination and staining were done using PSMA antibody. Tumor tissue PSMA immunohistochemical staining was scored semi-quantitatively with the modified quartile approach. Negative staining was scored 0, >0% and ≤25% tissue expression was considered weak (score 1), >25% and ≤50% tissue expression was considered mild (score 2), >50% and ≤75% tissue expression was considered moderate (score 3), and >75% tissue expression was considered strong (score 4).

Results

Eighty-eight patients (55 males, 33 females) were included in the study. Forty-eight patients had pleomorphic adenoma (PA), 35 had Warthin's tumor (WT), two had mucoepidermoid carcinoma, two had adenoid cystic carcinoma, and one had squamous cell carcinoma. There was statistically significant difference in terms of PSMA expression between PA and WT (p=0.003). PSMA expression was high in PA and absent in WT.

Conclusion

PSMA is a potential source of inspiration for future studies on the development of novel diagnostic and theranostic investigations of salivary gland tumors. Prospective studies targeting intratumoral PSMA in salivary gland tumors should be planned.

The Therapeutic Landscape of Salivary Gland Malignancies-Where Are We Now?

Salivary gland malignancies (SGMs) account for less than 5% of new diagnoses in head and neck tumors. If feasible, surgery is the preferred treatment modality. Nevertheless, some malignancies have a tendency of recurrence, with possible distant metastasis. Alternative treatment strategies, such as primary radiation or chemotherapeutics, often present low response rates. As a result, there is an unmet need for novel therapeutic approaches. Nowadays, target-based therapies (e.g., small inhibitors and immunotherapy) are used by the medical oncologist for possible treatment of advanced SGMs. Based on recent published trials, some novel treatments may provide additional disease control for some patients. However, sample sizes are small, the general findings are unsatisfactory, and a lot of uncertainties remain to be elucidated. Nevertheless, research shows that patients do not benefit from blind administration of systemic treatments and therefore a more personalized approach is highly needed. The aim of this review paper is to summarize the most recent advances in the biological understanding and molecular pathways of salivary gland cancers, the association of these pathways with the current treatments used and their implications for more personalized targeted-based therapies.

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.

PSMA Radioligand Uptake as a Biomarker of Neoangiogenesis in Solid Tumours: Diagnostic or Theragnostic Factor?

Due to its overexpression on the surface of prostate cancer cells, prostate-specific membrane antigen (PSMA) is a relatively novel effective target for molecular imaging and radioligand therapy (RLT) in prostate cancer. Recent studies reported that PSMA is expressed in the neovasculature of various types of cancer and regulates tumour cell invasion as well as tumour angiogenesis. Several authors explored the role of diagnostic and therapeutic PSMA radioligands in various malignancies. In this narrative review, we describe the current status of the literature on PSMA radioligands' application in solid tumours other than prostate cancer to explore their potential role as diagnostic or therapeutic agents, with particular regard to the relevance of PSMA radioligand uptake as neoangiogenetic biomarker. Hence, a comprehensive review of the literature was performed to find relevant articles on the applications of PSMA radioligands in non-prostate solid tumours. Data on the general, methodological and clinical aspects of all included studies were collected. Forty full-text papers were selected for final review, 8 of which explored PSMA radioligand PET/CT performances in gliomas, 3 in salivary gland malignancies, 6 in thyroid cancer, 2 in breast cancer, 16 in renal cell carcinoma and 5 in hepatocellular carcinoma. In the included studies, PSMA radioligand PET showed promising performance in patients with non-prostate solid tumours. Further studies are needed to better define its potential role in oncological patients management, especially in those undergoing antineoangiogenic therapies, and to assess the efficacy of PSMA-RLT in this clinical context.

A pilot study of 68 Ga-PSMA-617 PET/CT imaging and 177Lu-EB-PSMA-617 radioligand therapy in patients with adenoid cystic carcinoma

Background

This pilot study was designed to evaluate the diagnostic value of ⁶⁸ Ga-PSMA-617 and ¹⁸F-FDG PET/CT in adenoid cystic carcinoma (ACC) and to assess the safety and therapeutic response to PSMA radioligand therapy (RLT) in ACC patients.

Methods

Thirty patients pathologically diagnosed with ACC were recruited into the cohort. Each patient underwent ⁶⁸ Ga-PSMA-617 and ¹⁸F-FDG PET/CT within 1 week. The number and SUVmax of PET-positive lesions were recorded and compared. Four patients accepted RLT using ¹⁷⁷Lu-EB-PSMA-617, in a dosage of approximately 1.85 GBq (50 mCi) per cycle for up to 3 cycles.

Results

Compared with ¹⁸F-FDG, ⁶⁸ Ga-PSMA-617 revealed more PET-positive extrapulmonary tumors (157 vs. 141, P = 0.016) and higher SUVmax (8.8 ± 3.6 vs. 6.4 ± 4.2, P = 0.027). However, ⁶⁸ Ga-PSMA-617 revealed less PET-positive pulmonary lesions (202 vs. 301, P < 0.001) and lower SUVmax of tumors (3.1 ± 3.0 vs. 4.2 ± 3.9, P < 0.001) than ¹⁸F-FDG. The combination of ⁶⁸ Ga-PSMA-617 and ¹⁸F-FDG can detect 469 PET-positive lesions, which was superior to each alone (469 vs. 359 vs. 442, P < 0.001). Two patients achieved remarkable response after PSMA RLT, while the other two patients showed reduced tumor uptake of recurrent foci, lung and liver metastases, whereas increased SUVmax of bone metastases.

Conclusions

⁶⁸ Ga-PSMA-617 PET/CT is a valuable imaging modality for the detection of ACC and combining with ¹⁸F-FDG PET/CT will achieve a higher detection efficiency. PSMA RLT may be a promising treatment for ACC and is worth of further investigation.

Trial registration: Diagnosis of Adenoid Cystic Carcinoma on ⁶⁸ Ga-PSMA-617 PET-CT and Therapy With ¹⁷⁷Lu-EB-PSMA-617 (NCT04801264, Registered 16 March 2021, retrospectively registered).

URL of registry: https://clinicaltrials.gov/ct2/show/NCT04801264.

PSMA PET Imaging and Therapy in Adenoid Cystic Carcinoma and Other Salivary Gland Cancers: A Systematic Review

Simple Summary

Adenoid cystic carcinoma (ACC) and other salivary gland cancers (SGC) are rare conditions with limited treatment options when they recur or spread to other parts of the body. There is increasing interest in the interaction of radioactive labeled proteins 68Gallium- Prostate Specific Membrane Antigen (68Ga-PSMA) with their corresponding receptors on tumor cells (PSMA receptor) which can be detected on scans. This innovation has created diagnostic and therapeutic progress in management of metastatic prostate cancer. These interactions are also found in SGCs though studies are currently limited. Our systematic review aims to collate available published scientific information on this technology to better inform its potential use, pitfalls and its future directions as a diagnostic and therapeutic option in SGCs. We concluded that the 68Ga-PSMA scans can be useful in detecting ACC and SGC not detected on standard radioimaging and that small studies have shown the therapeutic potential of this innovation in advanced or metastatic ACC and SGC.

Abstract

Adenoid cystic carcinoma (ACC) and other salivary gland cancers (SGCs) are rare tumors where application of prostate specific membrane antigen (PSMA) positron emission tomography (PET) and PSMA radioligand therapy have yet to be studied extensively. This review explores the role of PSMA PET imaging and therapy as a theranostic tool for ACC and other SGCs based on current literature. A comprehensive literature search on PubMed and Embase was performed. All relevant studies containing information on PSMA PET imaging in ACC and SGC were included. Ten studies (one prospective, three retrospective, five case reports and one review paper) were included. For ACC, the mean maximum standardized uptake value (SUVmax) for local recurrence and distant metastases ranged from 2.41 to 13.8 and 2.04 to 14.9, respectively. In SGC, the meanSUVmax ranged from 1.2–12.50. Most studies observed PSMA expression positivity on immunohistochemistry (IHC) when there was PSMA PET uptake. PSMA PET was able to detect lesions not detected on standard imaging. Despite the small number of studies and wide intra-patient and inter-tumor variation of PSMA uptake in ACC and SGC, 68Gallium (68Ga)-PSMA PET has promising prospects as a diagnostic and radioligand therapeutic option. Further studies to answer the various theranostics considerations are required to guide its use in the real-world setting.

Current opinions on diagnosis and treatment of adenoid cystic carcinoma

Adenoid cystic carcinoma (ACC) is a rare malignant tumor derived mainly from the salivary glands, representing approximately 1% of all headandneck carcinomasand 10% of all salivary gland neoplasms. ACC displays a paradoxical behavioral combination of an indolent growth pattern but an aggressive progression, with local recurrence and distant metastasis. The propensity of ACC of the head and neck (ACCHN) for perineural invasion and its anatomical location, especially if it extends to the nasal cavity and paranasal sinuses, facilitates tumor involvement in the surrounding structures, such as the orbit, pterygopalatine fossa, Meckel'scave, and cavernous sinus, which can lead to skull base involvement and intracranial extension. Despite advances in molecular mechanisms and diagnostic imaging, ACC treatment remainschallenging due to the lack ofconsensuson treatment patterns. In this review, we aimed toprovideanupdatedinsight intothe understanding of ACCHN by focusing on clinical behavior, imaging diagnosis, pathological features, and therapeutic strategies. We reviewed the molecular mechanisms, especially in ACCHN with perineural invasion, and elaborated on treatment options, including chemotherapy, targeted therapies, and immunotherapy, to establish a comprehensive understanding of ACC to arrive at a policy for proper diagnosis, preoperative evaluation, and therapeutic strategies.

Beyond Surgical Treatment in Adenoid Cystic Carcinoma of the Head and Neck: A Literature Review

Introduction

Adenoid cystic carcinoma (AdCC) is a rare tumour as it accounts for about 10% of all salivary gland neoplasms. It occurs in all age groups with a predominance of women, but no risk factors have been identified to date. Although AdCC behaves as a slow-growing tumour, it is characterized by multiple and late recurrences. Therefore, we aim to update the knowledge of the treatment options in advanced and recurrent cases.

Materials and Methods

We performed a systematic literature review to provide a synthesis of the practical knowledge required for AdCC non-surgical management. Altogether, 99 out of the 1208 available publications were selected for analysis.

Results

AdCC is described as a basaloid tumour consisting of epithelial and myoepithelial cells. Immunohistochemistry is useful for diagnosis (PS100, Vimentin, CD117, CKit, muscle actin, p63) and for prognosis (Ki67). Identified mutations could lead to therapeutic opportunities (MYB-NFIB, Notch 1). The work-up is mainly based on neck and chest CT scan and MRI, and PET-CT with 18-FDG or PSMA can be considered. Surgical treatment remains the gold standard in resectable cases. Post-operative intensity modulated radiotherapy is the standard of care, but hadron therapy may be used in specific situations. Based on the available literature, no standard chemotherapy regimen can be recommended.

Conclusion

There is currently no consensus on the use of chemotherapy in AdCC, either concomitantly to RT in a postoperative setting or at a metastatic stage. Further, the available targeted therapies do not yet provide significant tumour response.

PET/CT With 68Ga-PSMA and 18F-FDG in Metastatic Adenoid Cystic Carcinoma: Report of 2 Cases

ABSTRACT

Adenoid cystic carcinoma (ACC) is a rare and slow-growing tumor, originating from salivary glands. Locoregional recurrence and distant metastasis of ACC can be visualized not only with 18F-FDG but also with 68Ga-PSMA PET/CT due to its high prostate-specific membrane antigen (PSMA) expression. We report 2 cases of metastatic ACC who underwent first 18F-FDG and then 68Ga-PSMA for staging and restaging.

First experiences with 177Lu-PSMA-617 therapy for recurrent or metastatic salivary gland cancer

Background

Advanced salivary gland cancers become difficult to treat when they are technically irresectable and radiotherapy limits are exceeded. There is also an unmet need to improve palliative systemic therapy. Salivary glands depict the Prostate-Specific Membrane Antigen (PSMA) on ⁶⁸Ga-PSMA-PET/CT, a transmembrane protein that is targeted for diagnosis and treatment of advanced prostate cancer. Some salivary gland carcinomas also express PSMA.

Methods

This study aimed to retrospectively evaluate the effectiveness of ¹⁷⁷Lu-PSMA-617 therapy for recurrent or metastatic salivary gland cancers, as a last resort treatment. Patients with serious tumour-related discomfort for whom no regular option was available were selected and critically re-assessed by the tumour board. Radionuclide therapy eligibility was confirmed when tumour targeting was greater than liver SUVmax on ⁶⁸Ga-PSMA-PET/CT. The protocol aimed at four cycles of 6.0–7.4 GBq ¹⁷⁷Lu-PSMA-617 every 6–8 weeks. Clinical response was evaluated by questionnaires and radiological response by ⁶⁸Ga-PSMA-PET/CT.

Results

Six patients were treated with ¹⁷⁷Lu-PSMA: four adenoid cystic carcinomas, one adenocarcinoma NOS and one acinic cell carcinoma. In two patients, radiological response was observed, showing either stable disease or a partial response, and four patients reported immediate relief of tumour-related symptoms. Most reported side effects were grade 1–2 fatigue, nausea, bone pain and xerostomia. Four patients prematurely discontinued therapy: three due to disease progression and one due to demotivating (grade 1) side-effects.

Conclusions

Palliative ¹⁷⁷Lu-PSMA therapy for salivary gland cancer may lead to rapid relief of tumour-associated discomfort and may even induce disease stabilization. It is safe, relatively well tolerated and can be considered when regular treatment options fail.

PSMA Expression in Differentiated Thyroid Cancer: Association With Radioiodine, 18FDG Uptake, and Patient Outcome

CONTEXT

Little is known about prostate-specific membrane antigen (PSMA) expression in patients with cervical involvement of differentiated thyroid cancer (DTC).

OBJECTIVE

We investigated PSMA expression in neck persistent/recurrent disease (PRD) using immunohistochemistry and the association with radioiodine (RAI) or 18-fluorodeoxyglucose (18FDG) uptake, and patient outcome.

DESIGN, SETTING, AND PATIENTS

Data from 44 consecutive DTC patients who underwent neck reoperation from 2006 to 2018 in a comprehensive cancer center.

MAIN OUTCOME MEASURE(S)

Immunostaining was performed with vascular endothelial marker CD31 and PSMA. PSMA expression was quantified using the immunoreactive score (IRS). RAI and 18FDG uptake were assessed before surgery using posttherapeutic RAI scintigraphy and 18FDG positron emission tomography with computed tomography. Mean follow-up after reintervention was 6.5 ± 3.7 years.

RESULTS

Thirty patients (68%) showed at least 1 PSMA-positive lesion (IRS ≥ 2) with similar proportions in RAI-positive and RAI-negative patients (75% vs 66%). In RAI-negative patients, however, the proportion of PSMA-positive disease (79% vs 25%, P < 0.01) and the mean IRS (4.0 vs 1.0, P = 0.01) were higher in 18FDG-positive than in 18FDG-negative patients. Furthermore, mean IRS was higher in patients ≥ 55 years, large primary tumors (>40 mm) or aggressive subtypes, and was correlated with structural disease at last follow-up. Strong PSMA expression (IRS ≥ 9) was associated with shorter progression-free survival (PFS).

CONCLUSIONS

Our findings show that PSMA expression was present in two-thirds of patients with neck PRD, that it was related to poor prognostic factors and that very high expression was associated with poorer PFS. This preliminary study may offer new perspectives for the management of RAI-refractory DTC.

Salivary Gland Cancers

Salivary gland carcinomas are a rare and heterogenous group of cancers with varying underlying biology and clinical behavior. A quickly evolving body of data has advanced the understanding of these tumors, leading to effective therapeutics for several histologic subtypes. Biologically rational clinical trials have developed from an understanding of MYB and NOTCH signaling in adenoid cystic carcinoma. The recognition of androgen receptor signaling and HER2-targeted therapy has offered therapeutic options in non-ACC salivary cancers. The use of TRK inhibitors in salivary secretory carcinoma has led to exceptional responses. Immunotherapy is an exciting new therapeutic avenue that requires further exploration.

Patterns of care analysis for salivary gland cancer: a survey within the German Society of Radiation Oncology (DEGRO) and recommendations for daily practice

Background

Salivary gland cancer (SGC) is rare and a heterogeneous type of cancer. Prospective randomized trials are lacking. No guideline focusing on standard procedures of radiotherapy (RT) in the treatment of SGC exists. Therefore, we surveyed the members of the German Society of Radiation Oncology (DEGRO) to gain information about current therapeutic strategies of SGC.

Methods

An anonymous questionnaire was designed and made available on the online platform umfrageonline.com. The corresponding link was sent to all DEGRO members who provided their user data for contact purposes. Alternatively, a PDF printout version was sent. Frequency distributions of responses for each question were calculated. The data were also analyzed by type of institution.

Results

Sixty-seven responses were received, including answers from 21 university departments, 22 non-university institutions, and 24 radiation oncology practices. Six participants reported that their departments (practice: n = 5, non-university hospital: n = 1) did not treat SGC, and therefore the questionnaire was not completed. Concerning radiation techniques, target volume definition, and concomitant chemotherapy, treatment strategies varied greatly among the participants. Comparing university vs. non-university institutions, university hospitals treat significantly more patients with SGC per year and initiated more molecular pathological diagnostics.

Conclusion

SGC represents a major challenge for clinicians, as reflected by the inhomogeneous survey results regarding diagnostics, RT approaches, and systemic therapy. Future prospective, multicenter clinical trials are warranted to improve and homogenize treatment of SGC and to individualize treatment according to histologic subtypes and risk factors.

Supplementary Information

The online version of this article (10.1007/s00066-021-01833-x) contains supplementary material, which is available to authorized users.

Immunohistochemical Reactivity of Prostate-Specific Membrane Antigen in Salivary Gland Tumors

Prostate-specific membrane antigen (PSMA) is a transmembrane glycoprotein that is overexpressed in the prostate gland and prostate cancer. PSMA has been recently used in positron emission tomography/computed tomography (PET/CT) imaging and targeted alpha-radiation therapy (TAT) for prostate cancer. Recently, the tubarial gland, a type of minor salivary gland that is described as a new organ situated in the pharynx, is reported to express PMSA. Here, we studied the expression of PSMA in common benign and malignant salivary gland tumors. We performed immunohistochemistry for PSMA in 55 salivary gland tumors comprising 10 pleomorphic adenomas, 10 Warthin tumors, 9 basal cell adenomas, 9 adenoid cystic carcinomas, 9 mucoepidermoid carcinomas, and 8 salivary duct carcinomas. PSMA was expressed in 97% of benign tumors and 77% of malignant tumors. Moreover, PSMA was expressed in 59% of normal salivary glands adjacent to the tumor. PSMA is relatively expressed in salivary gland tumors and salivary glands. Therefore, salivary gland neoplasm, and normal salivary gland, possibly demonstrate the accumulation of PSMA in PET/CT. Thus, we need to monitor the side effects in the salivary glands during TAT for prostate cancer.

Value of 18F-PSMA-PET/MRI for Assessment of Recurring Ranula

We report the case of a 6-year-old patient with suspected recurrence of a plunging ranula in clinical and ultrasonographic examination. Surgical resection of the left submandibular and sublingual glands had already been performed. Since persistent glandular tissue could not be excluded with certainty via MRI, we expanded diagnostics by performing a PET/MRI using a head and neck imaging protocol and the radiotracer ¹⁸F-PSMA-1007, which is physiologically expressed by salivary gland tissue. The ¹⁸F-PSMA-PET/MRI provided evidence of a cystically transformed, diminishing seroma in the left retro-/submandibular region. No ¹⁸F-PSMA expressing glandular tissue could be detected in the area of resection, excluding a relapse of a plunging ranula. As a consequence, we opted for a conservative treatment without further surgical intervention. We conclude that a simultaneous ¹⁸F-PSMA-PET/MRI is a comprehensive imaging modality, which can help to rule out persistent salivary tissue and recurring plunging ranula. It is a useful tool to facilitate the decision making of surgical interventions.

Dedicated Verification of an Accessory Parotid Gland via Minimal-Activity PSMA-PET/CT

Gallium-68-labeled prostate-specific membrane antigen ligands are not only established radiopharmaceuticals for staging of prostate cancer but also accumulate physiologically in nonprostate organs, including the salivary glands. We show the converted application of prostate-specific membrane antigen -positron emission tomography/computed tomography (PSMA-PET/CT) as a dedicated method to depict salivary gland tissue using a region-focused, low-dose protocol. An accessory parotid gland at the right buccal region could be confirmed; therefore, further diagnostic or invasive therapeutic steps were not necessary.

PSMA radioligand therapy for solid tumors other than prostate cancer: background, opportunities, challenges, and first clinical reports

In the past decade, a growing body of literature has reported promising results for prostate-specific membrane antigen (PSMA)-targeted radionuclide imaging and therapy in prostate cancer. First clinical studies evaluating the efficacy of [¹⁷⁷Lu]Lu-PSMA radioligand therapy (PSMA-RLT) demonstrated favorable results in prostate cancer patients. [¹⁷⁷Lu]Lu-PSMA is generally well tolerated due to its limited side effects. While PSMA is highly overexpressed in prostate cancer cells, varying degrees of PSMA expression have been reported in other malignancies as well, particularly in the tumor-associated neovasculature. Hence, it is anticipated that PSMA-RLT could be explored for other solid cancers. Here, we describe the current knowledge of PSMA expression in other solid cancers and define a perspective towards broader clinical implementation of PSMA-RLT. This review focuses specifically on salivary gland cancer, glioblastoma, thyroid cancer, renal cell carcinoma, hepatocellular carcinoma, lung cancer, and breast cancer. An overview of the (pre)clinical data on PSMA immunohistochemistry and PSMA PET/CT imaging is provided and summarized. Furthermore, the first clinical reports of non-prostate cancer patients treated with PSMA-RLT are described.

Adenoid cystic carcinoma: a review of clinical features, treatment targets and advances in improving the immune response to monoclonal antibody therapy

The natural history of adenoid cystic carcinoma (ACC) is relentless, defined by treatment failure heralded by locoregional recurrence and distant metastatic disease. In this review, we present an update of clinical features, molecular classification, current targeted therapies, immune landscapes and novel treatment targets with their respective clinical trials. The presented results are defined by a lack of overall response rate and limited progression free survival, with restriction to stable disease. In addition, ACC is resistant to immune checkpoint inhibition due to low tumour immunogenicity and lack of PD-L1 expression. Here we present a new prospective research paradigm for ACC, including the potential to target prostate specific membrane antigen (PSMA) and the potential for manipulation of target receptors in the clinic. The presentation of this review aims to promote future research to improve response rates and outcomes for therapeutics undergoing clinical trial in ACC.

A role of PSMA PET/CT in multimodality imaging approach in adenoid cystic carcinoma

Adenoid cystic carcinoma is a rare disease and characterised by slow but unrelenting local progression and risk of haematogenous metastases. We present a case of locally unresectable disease where PSMA PET/CT provided complementary staging and early treatment response assessment.

68Ga-Prostate-Specific Membrane Antigen-11-Avid Cardiac Metastases in a Patient With Adenoid Cystic Carcinoma, A Rare Presentation of a Rare Cancer

Adenoid cystic carcinoma is a rare cancer that arises from secretory glands. Metastases are mainly seen in the lungs and bones. Cardiac metastases are extremely rare; only 1 case has previously been described. In this patient, cardiac metastases were suspected based on CT imaging. Tumor imaging by Ga-prostate-specific membrane antigen (PSMA)-11 PET is mainly used in prostate cancer patients but is also of interest in adenoid cystic carcinoma patients because of high PSMA-ligand uptake in salivary glands. Ga-PSMA-11 PET imaging supported the suspicion of cardiac metastases, because the cardiac lesions showed similar tracer uptake compared with other metastases.

Prognostic value of PSMA, c-MET and E-cadherin in salivary duct carcinoma

OBJECTIVES

Salivary duct carcinoma (SDC) is a rare and aggressive subtype of salivary gland cancer. Androgen receptor (AR) (96%) and HER2 (29-46%) expression, and a high propensity for regional lymph node metastases are hallmarks of the disease. We hypothesized that c-MET, E-cadherin, PSMA tumor and PSMA neovascular expression may be prognostic factors in SDC.

MATERIALS AND METHODS

Expression levels of these proteins were established on tissue microarrays containing 165 primary SDC tumor specimens. Association with survival was studied with Kaplan-Meier curves, and univariable and multivariable Cox regression models. Furthermore, association with lymph node status, AR and HER2 expression, and gender was studied.

RESULTS

We found that patients with high PSMA tumor expression showed a significantly longer overall survival (OS) (median 83 vs. 43 months, P = 0.022), a trend towards a longer DFS (median 51 vs. 22 months, P = 0.094), and significantly reduced hazard ratio for death in the univariable Cox regression model (HR 0.46, P = 0.034). In the multivariable model only a high number of tumor-positive lymph nodes and high age (>80) at diagnosis were prognostic for poor OS. High PSMA tumor expression was also significantly associated with low N-stage (P = 0.001) and expression was higher in women versus men (P = 0.029). High PSMA tumor expression and E-cadherin loss were significantly associated with strong and weak AR-expression, respectively (P = 0.033 and P = 0.007). None of the factors were significantly associated with HER2 expression.

CONCLUSION

c-MET, E-cadherin, and tumor and neovascular PSMA expression are no independent prognostic factors in SDC.

Prostate-specific membrane antigen (PSMA) expression in adenoid cystic carcinoma of the head and neck

BACKGROUND

Treatment options for advanced head and neck adenoid cystic carcinoma (AdCC) are limited. Prostate-Specific Membrane Antigen (PSMA), a transmembrane protein that is known for its use in diagnostics and targeted therapy in prostate cancer, is also expressed by AdCC. This study aimed to analyse PSMA expression in a large cohort of primary, recurrent and metastasized AdCC of the head and neck.

METHODS

One hundred ten consecutive patients with histologically confirmed AdCC in the period 1990-2017 were included. An analysis was made of clinical details, revised pathology and semiquantitative immunohistochemical expression of PSMA on tissue microarray and whole slides. Associations of PSMA expression with clinicopathological parameters were explored and survival was analysed by multivariate Cox-proportional Hazard analysis.

RESULTS

PSMA expression was present in 94% of the 110 primary tumours, with a median of 31% positive cells (IQR 15-60%). Primary tumours (n = 18) that recurred (n = 15) and/or had metastases (n = 10) demonstrated 40, 60 and 23% expression respectively. Expression was not independently related to increased pathological stage, tumour grade, and the occurrence of locoregional recurrence or metastasis. After dichotomization, only primary tumour PSMA expression ≤10% appeared to be associated with reduced 10-years recurrence-free survival (HR 3.0, 95% CI 1.1-8.5, p = .04).

CONCLUSIONS

PSMA is highly expressed in primary, recurrent and metastatic AdCC of the salivary and seromucous glands. PSMA expression has no value in predicting clinical behaviour of AdCC although low expression may indicate a reduced recurrence-free survival. This study provides supporting results to consider using PSMA as target for imaging and therapy when other diagnostic and palliative treatment options fail.

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.

68Ga-PSMA-HBED-CC PET/CT imaging for adenoid cystic carcinoma and salivary duct carcinoma: a phase 2 imaging study

Rationale: Treatment options for recurrent and/or metastatic (R/M) adenoid cystic carcinoma (ACC) and salivary duct carcinoma (SDC), major subtypes of salivary gland cancer, are limited. Both tumors often show overexpression of prostate-specific membrane antigen (PSMA). In prostate cancer, PSMA-ligands labeled with ⁶⁸Ga or ¹⁷⁷Lu are used for imaging and therapy, respectively. Primary aim of this study in R/M ACC and SDC patients was to systematically investigate ⁶⁸Ga-PSMA-uptake by PET/CT imaging to determine if PSMA radionuclide therapy could be a treatment option.

Methods: In a prospective phase II study, PET/CT imaging was performed 1 h post injection of ⁶⁸Ga-PSMA-HBED-CC in 15 ACC patients and 10 SDC patients. Maximum standardized uptake values (SUV) were determined in tumor lesions. Immunohistochemical PSMA expression was scored in primary tumors and metastatic tissue. Standard imaging (MRI or CT) was performed for comparison.

Results: In ACC patients, SUV_max ranged from 1.1 to 30.2 with a tumor/liver-ratio >1 in 13 out of 14 evaluable patients (93%). In SDC patients, SUV_max ranged from 0.3 to 25.9 with a tumor/liver-ratio >1 in 4 out of 10 patients (40%). We found a large intra-patient inter-metastatic variation in uptake of ⁶⁸Ga-PSMA, and immunohistochemistry did not predict ligand uptake in ACC and SDC. Finally, PSMA-PET detected additional bone metastases compared to CT in 2 ACC patients with unexplained pain.

Conclusion: In 93% of ACC patients and 40% of SDC patients we detected relevant PSMA-ligand uptake, which warrants to study PSMA radionuclide therapy in these patients. Additionally, our data provide arguments for patient selection and treatment timing. Finally, PSMA-PET imaging has added diagnostic value compared to CT in selected patients.

Radionuclide Therapy With 177Lu-PSMA in a Case of Metastatic Adenoid Cystic Carcinoma of the Parotid

In vivo prostate-specific membrane antigen (PSMA) overexpression creates an opportunity for PSMA-directed theranostic approach in adenoid cystic carcinoma of the parotid. Herein, we illustrate a patient with metastatic PSMA-directed theranostic approach in adenoid cystic carcinoma of the parotid who had intense PSMA uptake on metastatic lesions, followed by radionuclide therapy with Lu-PSMA.

Advances and challenges in precision medicine in salivary gland cancer

Salivary gland cancer (SGC) is a rare malignancy consisting of 22 subtypes with different genetic, histological and clinical characteristics. This rarity and heterogeneity makes systemic treatment of recurrent or metastatic (R/M) disease challenging. Use of chemotherapy is scarcely studied and chemotherapy at best has moderate effects. New therapeutic strategies are therefore warranted, but advances made in SGC are lagging behind on advances made in more common cancers. By unraveling tumor characteristics of SGC, such as genetic alterations and protein expression profiles, therapeutic strategies tailored to the patient's tumor can be rationalized. This genomic profiling and mapping of immunohistochemical expression profiles is essential in the search for a suitable treatment approach. Thereby, it alleviates the paucity in systemic treatment options and can significantly alter the prognosis of patients with R/M SGC. This review aims to give a comprehensive overview of known genetic alterations and expression profiles amenable for targeted therapy in every histological subtype of SGC. We discuss the remaining knowledge gaps and the implications of these targets for future studies and personalized treatments, thereby aiding clinicians faced with this rare and heterogeneous type of cancer.

PSMA-Targeting Positron Emission Agents for Imaging Solid Tumors Other Than Non-Prostate Carcinoma: A Systematic Review

Despite its name, prostate-specific membrane antigen (PSMA) has been shown using immunohistochemistry (IHC) to also be over-expressed in the tumor neovasculature of a wide variety of solid tumors other than prostate carcinoma. Accordingly, positron-emitting radiolabeled small molecules targeting PSMA, initially developed for positron emission tomography in prostate carcinomas, are currently being explored for their staging and restaging potential as an alternative imaging modality in other solid tumor types where 18-F-fluorodeoxyglucose (FDG)-PET imaging has low diagnostic accuracy. In this paper, the currently available literature in this field is reviewed. Preliminary, mainly retrospective studies are encouraging, with evidence of improved diagnostic sensitivity and specificity in clear cell renal carcinoma, glioma, and hepatocellular carcinoma, leading to a change in patient management in several patients. However, the results published thus far warrant confirmation by larger prospective studies additionally assessing the longitudinal impact on patient outcomes.

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.

Avid 68Ga-PSMA Uptake in Accessory Submandibular Salivary Gland

Accessory submandibular salivary gland (ASSG) is an extremely rare variation of the submandibular salivary gland. We reported a 65-year-old man with prostate cancer underwent Ga-PSMA PET/CT for active surveillance. The images showed abnormal PSMA uptake adjacent to the submandibular salivary gland without abnormal activity distribution in the rest regions of the body. The lesion density was similar to that of the submandibular salivary gland. Pathological biopsy confirmed that it was an ASSG. Our case illustrates that ASSG is an addition benign cause of extraprostatic uptake of PSMA.

Brush border enzyme-cleavable linkers: Evaluation for reducing renal uptake of radiolabeled prostate-specific membrane antigen inhibitors

INTRODUCTION

Radiolabeled, low-molecular-weight prostate-specific membrane antigen (PSMA) inhibitors based on the Glu-ureido pharmacophore show promise for the detection and treatment of castration-resistant prostate cancer; however, high renal retention of activity, related in part to overexpression of PSMA in kidneys can be problematic. The goal of the current study was to investigate the use of brush border enzyme-cleavable linkers as a strategy for reducing kidney activity levels from radiolabeled PSMA inhibitors.

METHODS

PSMA-769 (6), a derivative of the prototypical PSMA inhibitor (((S)‑1‑carboxy‑5‑(4‑iodobenzamido)pentyl)carbamoyl)glutamate (12) modified to contain a Gly-Tyr linker, and its protected tin precursor (11) were synthesized starting from the basic pharmacophore molecule Lys-urea-Glu. An analogue of 6 containing d‑tyrosine in lieu of l‑tyrosine (PSMA-769-d-tyrosine) and the corresponding tin precursor (d-11) also were synthesized. Both radioiodinated and ²¹¹At-labeled 6 were synthesized by radiohalogenation of 11 and deprotection in situ. Similarly, radioiodinated d-6 was synthesized from d-11. Paired label biodistribution of [¹²⁵I]12 and [¹³¹I]6 was performed in normal mice and in SCID mice bearing both PC3 PIP (PSMA+) and PC3 flu (PSMA-) subcutaneous prostate carcinoma xenografts. The biodistribution of [¹³¹I]6 and [²¹¹At]6 was also evaluated in this tumor model. Biodistribution of the two radioiodinated diastereomers of 6 was evaluated in normal mice and urine samples were analyzed for the presence of 4‑iodohippuric acid.

RESULTS

Compounds [¹³¹I]6 and [²¹¹At]6 were synthesized from 11 in overall radiochemical yields of 32.5 ± 0.1% (n = 4) and 22% (n = 1), respectively; radiochemical purity was >95%. In normal mice, renal uptake of [¹³¹I]6 was 1.4-, 2.8- and 161-fold lower than that seen for co-injected [¹²⁵I]12 at 1 h, 4 h and 21 h, respectively. In tumor-bearing mice, kidney uptake of [¹³¹I]6 was similar to that for [¹²⁵I]12 (P > 0.05) at 1 h and 4 h but was 6- to 7-fold lower at 21 h; however, [¹³¹I]6 uptake in PC3 PIP tumors was also lower than that seen for [¹²⁵I]12 at 21 h (12.6 ± 3.4%ID/g vs. 36.8 ± 12.4%ID/g). Uptake of [²¹¹At]PSMA-769 in PC3 PIP tumors was slightly higher than that seen for [¹³¹I]PSMA-769 at 4 h (9.6 ± 1.6%ID/g versus 7.8 ± 1.6%ID/g; P = 0.002); its uptake in a number of normal tissues also was higher. In normal mice, kidney uptake of [¹²⁵I]PSMA-769 at 4 h was about 73% of that seen for [¹³¹I]PSMA-769-d-tyrosine. Activity in the urine of mice receiving [¹²⁵I]PSMA-769 contained mainly 4‑[¹²⁵I]iodohippuric acid while unmetabolized intact molecule was present in the case of [¹²⁵I]PSMA-769-d-tyrosine.

CONCLUSION

Use of this brush border enzyme-cleavable linker reduced kidney uptake and resulted in improved tumor:kidney uptake ratios. Although further structural improvements are needed, this linker approach might be useful as a component in strategies for reducing renal uptake of radiolabeled PSMA inhibitors.

Imaging of Nonprostate Cancers Using PSMA-Targeted Radiotracers: Rationale, Current State of the Field, and a Call to Arms

Prostate-specific membrane antigen (PSMA) is a type II transmembrane glycoprotein that is highly overexpressed on prostate cancer epithelial cells and for which there is a growing body of literature examining the role of small-molecule and antibody radiotracers targeted against this protein for prostate cancer detection and therapy. Despite its name, PSMA is also expressed, to varying degrees, in the neovasculature of a wide variety of nonprostate cancers; indeed, the pathology literature is replete with promising immunohistochemistry findings. Several groups have begun to correlate those pathology-level results with in vivo imaging and therapy in nonprostate cancers using the same PSMA-targeted agents that have been so successful in prostate cancer. The potential to leverage radiotracers targeted to PSMA beyond prostate cancer is a promising approach for many cancers, and PSMA-targeted agents may be able to supplement or fill gaps left by other agents. However, to date, most of the reported findings with PSMA-targeted radiotracers in nonprostate malignancies have been in case reports and small case series, and the field must adopt a more thorough approach to the design and execution of larger prospective trials to realize the potential of these promising agents outside prostate cancer.

Uptake of Prostate-Specific Membrane Antigen (PSMA) in adenoid cystic carcinoma - Is PSMA-PET-CT a helpful tool in radiation oncology?

This case report shows the high PSMA-uptake in a patient with an adenoid cystic carcinoma of the maxillary sinus. Due to the intense ligand-uptake additional information for target volume delineation was obtained and the Treatment plan for bimodal radiotherapy with carbon ions was adapted accordingly.