18F-PSMA 1007 Uptake in Brain Metastases From Breast Cancer

Brain metastasis: An insight into novel molecular targets for theranostic approaches

Brain metastases (BrM) are common malignant lesions in the central nervous system, and pose a significant threat in advanced-stage malignancies due to delayed diagnosis and limited therapeutic options. Their distinct genomic profiles underscore the need for molecular profiling to tailor effective treatments. Recent advances in cancer biology have uncovered molecular drivers underlying tumor initiation, progression, and metastasis. This, coupled with the advances in molecular imaging technology and radiotracer synthesis, has paved the way for the development of innovative radiopharmaceuticals with enhanced specificity and affinity for BrM specific targets. Despite the challenges posed by the blood-brain barrier to effective drug delivery, several radiolabeled compounds have shown promise in detecting and targeting BrM. This manuscript provides an overview of the recent advances in molecular biomarkers used in nuclear imaging and targeted radionuclide therapy in both clinical and preclinical settings. Additionally, it explores potential theranostic applications addressing the unique challenges posed by BrM.

Imaging Molecular Targets and Metabolic Pathways in Breast Cancer for Improved Clinical Management: Current Practice and Future Perspectives

Breast cancer is the most frequently diagnosed cancer and leading cause of cancer-related deaths worldwide. Timely decision-making that enables implementation of the most appropriate therapy or therapies is essential for achieving the best clinical outcomes in breast cancer. While clinicopathologic characteristics and immunohistochemistry have traditionally been used in decision-making, these clinical and laboratory parameters may be difficult to ascertain or be equivocal due to tumor heterogeneity. Tumor heterogeneity is described as a phenomenon characterized by spatial or temporal phenotypic variations in tumor characteristics. Spatial variations occur within tumor lesions or between lesions at a single time point while temporal variations are seen as tumor lesions evolve with time. Due to limitations associated with immunohistochemistry (which requires invasive biopsies), whole-body molecular imaging tools such as standard-of-care [18F]FDG and [18F]FES PET/CT are indispensable in addressing this conundrum. Despite their proven utility, these standard-of-care imaging methods are often unable to image a myriad of other molecular pathways associated with breast cancer. This has stimulated interest in the development of novel radiopharmaceuticals targeting other molecular pathways and processes. In this review, we discuss validated and potential roles of these standard-of-care and novel molecular approaches. These approaches' relationships with patient clinicopathologic and immunohistochemical characteristics as well as their influence on patient management will be discussed in greater detail. This paper will also introduce and discuss the potential utility of novel PARP inhibitor-based radiopharmaceuticals as non-invasive biomarkers of PARP expression/upregulation.

68Ga-PSMA Uptake in Brain Metastasis of Gastric Carcinoma

ABSTRACT

A 69-year-old man with a known history of gastric and prostate adenocarcinoma was referred to 68Ga-prostate-specific membrane antigen (PSMA) PET/CT for restaging due to biochemical recurrence of prostate cancer. 68Ga-PSMA PET/CT revealed tracer accumulation in the primary prostatic lesion, lymph node, bone metastases, and brain lesion, which was later confirmed on biopsy to be metastasis of gastric carcinoma. This case reminds us of the variable spectrum of 68Ga-PSMA uptake in prostatic and nonprostatic metastatic lesions, the potential pitfalls on PET/CT images in the workup of patients with concomitant malignancies.

Prostate-Specific Membrane Antigen as Target for Neuroimaging of Central Nervous System Tumors

Introduction. Positron emission tomography (PET) imaging with prostate-specific membrane antigen- (PSMA-) binding tracers has been found incidentally to demonstrate uptake in CNS tumors. Following the encouraging findings of several such case reports, there is a growing interest in the potential application of PSMA-targeted PET imaging for diagnostics, theranostics, and monitoring of CNS tumors. This is a systematic literature review on PSMA-binding tracers in CNS tumors. Methods. A PubMed search was conducted, including preclinical and clinical reports. One hundred and twelve records were identified, and after screening, 56 were included in the final report. Results. Tissue studies demonstrated PSMA expression in tumor vascular endothelial cells, without expression in normal brain tissue, though the extent and intensity of staining varied by anti-PSMA antibody and methodology. Most included studies reported on gliomas, which showed strong PSMA ligand uptake and more favorable tumor to background ratios than other PET tracers. There are also case reports demonstrating PSMA ligand uptake in prostate cancer brain metastases, nonprostate cancer brain metastases, and meningiomas. We also review the properties of the various PSMA-binding radiotracers available. Therapeutic and theranostic applications of PSMA-binding tracers have been studied, including labeled alpha- and beta-ray emitting isotopes, as well as PSMA targeting in directing MRI-guided focused ultrasound. Conclusions. There is a potential application for PSMA-targeted PET in neuro-oncology as a combination of diagnostic and therapeutic use, as a theranostic modality for managing CNS tumors. Further research is needed regarding the mechanism(s) of PSMA expression in CNS tumors and its differential performance by tumor type.

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.

Incidental Detection of Radiotracer Uptake in Intracranial Dermoid Cyst on 18F-Prostate-Specific Membrane Antigen PET/CT During Staging for Prostate Carcinoma

ABSTRACT

A 68-year-old man underwent 18F-prostate-specific membrane antigen (PSMA) PET/CT for staging of a newly diagnosed prostate adenocarcinoma. Unexpectedly, PET/CT revealed high focal 18F-PSMA brain uptake, which initially was suspected for a brain metastasis. Corresponding CT and MRI scans revealed characteristic imaging features of an intracranial dermoid cyst at this site. This is an exceptional location for a dermoid cyst, which had been followed up conservatively with no substantial changes. This case shows that dermoid cyst should be added to the reported list of benign neoplasms that shows "false-positive" PSMA uptake during evaluation of patients with prostate carcinoma, representing a potential interpretative pitfall.

Recurrent Brain Metastasis of Triple Negative Breast Cancer With High Uptake in 68Ga-PSMA-11 PET/CT

ABSTRACT

Triple negative breast cancer (TNBC) is characterized by poor prognosis and limited response to standard treatments. Although 18F-FDG PET/CT is frequently used in staging and restaging, in some cases, it may be insufficient considering tumor heterogeneity. Prostate-specific membrane antigen (PSMA) has been reported to be overexpressed in many types of cancer due to tumor-associated neovascularization. 68Ga-PSMA-11 PET/CT can be used to demonstrate radionuclide therapy option as well as detection of primary tumor and recurrence in TNBC. We present a 47-year-old woman with TNBC having recurrent brain metastasis with avid PSMA receptor activity versus low FDG uptake.

Duodenal Adenocarcinoma Mimicking Metastasis of Prostate Cancer on 18F-Prostate-Specific Membrane Antigen-1007 PET/CT

A 76-year-old man with dyspnea (initial prostate-specific antigen [PSA]: 216 ng/mL) underwent F-FDG PET/CT, with uptake in the prostate, lymph nodes, fifth thoracic vertebra (T5), and cricoid cartilage. A biopsy revealed prostate adenocarcinoma (Gleason score 4 + 5, cT4 N1 M1). On initiation of combined androgen blockade therapy, PSA value decreased. However, 4 years later, in a castration-resistant state (PSA 2.14 ng/mL), CT and bone scintigraphy revealed a duodenal tumor and T5 metastasis. F-prostate-specific membrane antigen-1007 PET/CT showed uptake in the already known T5 metastasis (SUVmax, 33.55) and even in the duodenal tumor (16.55). The latter was histologically diagnosed as duodenal adenocarcinoma.

Current landscape and future perspectives in preclinical MR and PET imaging of brain metastasis

Brain metastasis (BM) is a major cause of cancer patient morbidity. Clinical magnetic resonance imaging (MRI) and positron emission tomography (PET) represent important resources to assess tumor progression and treatment responses. In preclinical research, anatomical MRI and to some extent functional MRI have frequently been used to assess tumor progression. In contrast, PET has only to a limited extent been used in animal BM research. A considerable culprit is that results from most preclinical studies have shown little impact on the implementation of new treatment strategies in the clinic. This emphasizes the need for the development of robust, high-quality preclinical imaging strategies with potential for clinical translation. This review focuses on advanced preclinical MRI and PET imaging methods for BM, describing their applications in the context of what has been done in the clinic. The strengths and shortcomings of each technology are presented, and recommendations for future directions in the development of the individual imaging modalities are suggested. Finally, we highlight recent developments in quantitative MRI and PET, the use of radiomics and multimodal imaging, and the need for a standardization of imaging technologies and protocols between preclinical centers.

Non-prostate uptake on 18F-PSMA-1007 PET/CT: a case of myeloma

Prostate-specific membrane antigen (PSMA), a glycoprotein that is highly expressed in prostate cancer, has been used as a target for molecular radiotherapy as well as imaging. Over the last couple of years, ¹⁸F-PSMA gained popularity due to its longer half-life (110 min) compared to gallium ⁶⁸Ga-PSMA (68 min). This has helped the dissemination beyond large metropolitan centres. In addition, due to the low background activity in the urinary bladder (1.2% injected dose over 2 h compared to 10% injected dose over 2 h for ⁶⁸Ga), ¹⁸F-PSMA helps detect local recurrence or spread to pelvic nodes more readily as lesions are not masked by physiological urinary excretion.

Despite excellent sensitivities of PSMA positron emission tomography modalities, it is noteworthy that PSMA expression is not specific to the prostate. A variety of normal tissues express PSMA with intense uptake noted in salivary glands, lacrimal glands, the liver, spleen, pancreas, small intestine, bladder and renal cortex.

In this case report, we describe an example of non-prostatic PSMA uptake in a patient imaged with ¹⁸F-PSMA-1007 positron emission tomography/CT that showed an avid lytic lesion in manubrium. The patient was subsequently proven by biopsy to have myeloma. Our case report illustrates a potential pitfall when imaging patients with ¹⁸F PSMA-1007 and adds to the growing body of literature of non-prostatic uptake of PSMA and highlights the need for reporters to be aware of this uptake.

Incidental Detection of Malignant Melanoma Brain Recurrence on 68Ga-Prostate-Specific Membrane Antigen PET/CT

A 76-year-old man with a prior medical history of resected malignant melanoma of the skull underwent Ga-prostate-specific membrane antigen (PSMA) PET/CT due to rising tumor markers of a known prostate carcinoma. Unexpected high Ga-PSMA brain uptake was encountered around the surgical cavity in the skull with initially no specific structural changes on anatomical imaging. Successive CT and MRI eventually revealed local melanoma brain recurrence at this site. This interesting case demonstrates the diagnostic potential of Ga-PSMA PET/CT imaging for detection of malignant melanoma brain recurrence.