Pitfalls in Ga-68-PSMA-PET/CT: incidental finding of parathyroid adenoma

Parathyroid Adenoma Detected in 68Ga-PSMA PET/CT but Not in the Dedicated Imaging Modalities

BACKGROUND

Primary hyperparathyroidism is a common endocrine disorder characterised by excessive parathormone secretion that results in hypercalcemia, primarily caused by parathyroid adenoma. Accurate localisation of hyperfunctioning tissue is essential for curative surgical treatment. Although conventional imaging modalities like ultrasonography and 99mTc-MIBI scintigraphy (SPECT) along with 18F-fluorocholine PET/CT are commonly employed, there are cases with false-negative imaging results.

CASE PRESENTATION

This case report presents a patient with primary hyperparathyroidism and a parathyroid adenoma detected solely through 68Ga-PSMA-11 PET/CT, typically used for prostate cancer diagnosis. The lesion observed in the PET/CT was confirmed as a parathyroid adenoma through laboratory evaluation, while other imaging techniques failed to detect it.

CONCLUSIONS

This finding suggests that the PSMA ligands' particular affinity for neovascularisation in focal changes may facilitate the visualisation of parathyroid adenomas. The utilisation of 68Ga-PSMA-11 PET/CT in primary hyperparathyroidism could potentially improve the preoperative localization of parathyroid adenomas when conventional imaging methods are inconclusive.

Nuclear medicine imaging modalities to detect incidentalomas and their impact on patient management: a systematic review

PURPOSE

This systematic review aims to investigate the role of nuclear imaging techniques in detecting incidentalomas and their impact on patient management.

METHODS

Following PRISMA guidelines, a comprehensive literature search was conducted from February to May 2022. Studies in English involving patients undergoing nuclear medicine studies with incidental tumor findings were included. Data on imaging modalities, incidentaloma characteristics, management changes, and follow-up were extracted and analyzed.

RESULTS

Ninety-two studies involving 64.884 patients were included. Incidentalomas were detected in 611 cases (0.9%), with thyroid being the most common site. PET/CT with FDG and choline tracers showed the highest incidentaloma detection rates. Detection of incidentalomas led to a change in therapeutic strategy in 59% of cases. Various radiotracers demonstrated high sensitivity for incidentaloma detection, particularly in neuroendocrine tumors and prostate cancer.

CONCLUSION

Nuclear imaging techniques play a crucial role in detecting incidentalomas, leading to significant changes in patient management. The high sensitivity of these modalities highlights their potential in routine oncology follow-up protocols. Future directions may include enhancing spatial resolution and promoting theranostic approaches for improved patient care.

Incidental Detection of Parathyroid Adenoma on 18F-PSMA PET/CT

ABSTRACT

A 70-year-old man, diagnosed with prostate cancer, was referred to the Department of Nuclear Medicine for tumor staging with prostate-specific membrane antigen (PSMA) PET/CT. High PSMA uptake was observed in the prostate without PSMA-avid lymph nodes or distant metastases. Coincidentally, a PSMA-avid nodule was observed dorsal to the right thyroid lobe. A complementary 4-dimensional CT showed a round nodule of 18 mm with quick contrast enhancement well demarcated from its surroundings. Blood tests revealed elevated serum calcium and parathyroid hormone consistent with primary hyperparathyroidism. Subsequently, parathyroidectomy was performed, and histopathological examination of the nodule confirmed a parathyroid adenoma.

Mild 68Ga PSMA-11 Uptake in Incidental Pituitary Adenoma

A 76-year-old man with metastatic prostate cancer was referred to ⁶⁸Ga prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) for restaging. A consecutive ¹⁸F-fluorodeoxyglucose (FDG) PET/CT was performed due to the history of lung cancer in the left lung treated with stereotactic radiotherapy. Intense ¹⁸F-FDG uptake was detected in the pituitary gland despite the mild uptake of ⁶⁸Ga PSMA. Contrast-enhanced magnetic resonance imaging confirmed pituitary adenoma.

Cancers and Benign Processes on 68Ga PSMA PET-CT Imaging Other than Prostate Cancer

Background  Imaging plays an important role in the evaluation of prostate cancer patients. In recent years, much attention has been focused on gallium 68 prostate-specific membrane antigen positron emission tomography-computed tomography ( ⁶⁸ Ga PSMA PET-CT) in prostate cancer patients and has been widely used for staging, restaging, and therapy response for these patients. The aim of this study was to report ⁶⁸ Ga PSMA PET-CT in other cancers and benign processes incidentally detected on ⁶⁸ Ga PSMA PET-CT in patients with prostate cancer.

Materials and Methods  A total of 600 ⁶⁸ Ga PSMA PET-CT scans were performed for initial staging, restaging, detection of suspected recurrence, and therapy response in prostate cancer patients between December 2018 and June 2020. A total of 38 patients with histopathologically proven prostate cancer were included in the current study with other malignancies and benign processes. Mainly histopathology in most of cases and clinical and radiological follow-up in few cases after PET/CT scanning served as the standard of reference.

Results  A total of 38 patients (age range: 52–85 years; mean age: 68.6) with prostate cancer final histopathology results were included in the study. A total of 51 lesion sites were evaluated in 38 patients. Forty-one lesion regions of these 51 regions were based on histopathological diagnosis, whereas 10 of them were based on clinical follow-up and conventional radiological follow-up as differential criteria. Thirty of 51 lesion regions were evaluated as malignant and 21 were benign lesions. The most common ⁶⁸ Ga PSMA ligand avid malignancy was lung adenocarcinoma (6/38).

Conclusions  Prostate-specific membrane antigen (PSMA) is a cell surface glycoprotein and mainly expressed in prostate epithelium. ⁶⁸ Ga PSMA PET-CT imaging is very sensitive and specific imaging modality in prostate cancer patients. However, other malignancies and some benign processes may also have ⁶⁸ Ga PSMA ligand avidity and some prostate cancer metastases may imitate other malignancies.

The utility of radiolabeled PSMA ligands for tumor imaging

Prostate-specific membrane antigen (PSMA) is a glycosylated type-II transmembrane protein expressed in prostatic tissue and significantly overexpressed in several prostate cancer cells. Despite its name, PSMA has also been reported to be overexpressed in endothelial cells of benign and malignant non-prostate disease. So its clinical use was extended to detection, staging, and therapy of various tumor types. Recently small molecules targeting PSMA have been developed as imaging probes for diagnosis of several malignancies. Preliminary studies are emerging improved diagnostic sensitivity and specificity of PSMA imaging, leading to a change in patient management. In this review, we evaluated the first preclinical and clinical studies on PSMA ligands resulting future perspectives radiolabeled PSMA in staging and molecular characterization, based on histopathologic examinations of PSMA expression.

Current status of radioligand therapy and positron-emission tomography with prostate-specific membrane antigen

Prostate-specific membrane antigen (PSMA) is a transmembrane glycoprotein highly expressed by prostate cancer cells. PSMA-based radioligand therapy (RLT) emerged as a promising therapeutic option for prostate cancer in the early 2000s, and has been clinically validated with great enthusiasm during these past two decades. Last year, the European Association of Nuclear Medicine (EANM) published the procedure guidelines for the safe clinical practice of Lutetium-177 (¹⁷⁷Lu)-labelled PSMA RLT. In addition, PSMA RLT with alpha-ray-emitting radioisotopes has been also developed recently. Following the clinical use of ¹⁷⁷Lu-PSMA RLT, PSMA-targeted positron-emission tomography (PET) with Gallium-68 (⁶⁸Ga) has been performed inevitably for “theranostics” for the last decade; prostate cancer is going to be treated with PSMA-RLT based on the diagnosis by PSMA-PET. Furthermore, the diagnostic usefulness of ⁶⁸Ga-PSMA PET has been documented in various diseases beyond prostate cancer more recently. Regrettably, Japan is behind European countries and the United States in this field, and has just made a belated start of their clinical trials. In this review article, we briefly overviewed the current status of PSMA RLT and PSMA PET. We hope that this topic will be a particular focus of attention for most ANM readers in Japan, and that our efforts will help to facilitate the early approval of PSMA RLT and PSMA PET by the Japanese government even if only slightly.

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.

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.