Heterogeneity of 68Ga-PSMA PET/CT Uptake in Fibrous Dysplasia

Incidental 68 Ga-PSMA Uptake in the Benign Enchondroma-A Rare Finding on 68 Ga-PSMA PET/CT

ABSTRACT

68 Ga-PSMA (prostate-specific membrane antigen)-HBED-CC (N,N'-bis[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-N,N'-diacetic acid) PET/CT is the new advancement in oncological imaging. However, false-positive uptake can be seen in benign lesions on 68 Ga-PSMA PET/CT. We describe a rare case of intense 68 Ga-PSMA uptake in an enchondroma confirmed on MRI.

Musculoskeletal pitfalls in 68Ga-PSMA PET/CT

Prostate-specific membrane antigen (PSMA) is a transmembrane protein expressed in normal prostate cells and overexpressed in prostate cancer. Consequently, it is an important tool in the evaluation of prostate cancer, including the staging of high-risk patients and the assessment of biochemical recurrence. Despite the "specific" designation, benign musculoskeletal conditions, such as fractures, osteodegenerative changes, and fibrous dysplasia, can also show PSMA uptake, which can lead to misinterpretation of the imaging findings. Therefore, radiologists must be aware of these potential pitfalls, understand their causes, and fully analyze their morphologic features on unfused computed tomography (CT) and magnetic resonance imaging scans to correctly interpret the examination. In this pictorial essay, we review the basic characteristics of the 68Ga-PSMA positron-emission tomography/CT (PET/CT) radiotracer, discuss potential causes of false-positive findings on 68Ga-PSMA PET/CT in the musculoskeletal system, and illustrate the corresponding imaging findings.

Multidisciplinary management of spinal metastases: what the radiologist needs to know

The modern management of spinal metastases requires a multidisciplinary approach that includes radiation oncologists, surgeons, medical oncologists, and diagnostic and interventional radiologists. The diagnostic radiologist can play an important role in the multidisciplinary team and help guide assessment of disease and selection of appropriate therapy. The assessment of spine metastases is best performed on MRI, but imaging from other modalities is often needed. We provide a review of the clinical and imaging features that are needed by the multidisciplinary team caring for patients with spine metastases and stress the importance of the spine radiologist taking responsibility for synthesizing imaging features across multiple modalities to provide a report that advances patient care.

Update of PSMA Theranostics in Prostate Cancer: Current Applications and Future Trends

There is now an increasing trend for targeting cancers to go beyond early diagnosis and actually improve Progression-Free Survival and Overall Survival. Identifying patients who might benefit from a particular targeted treatment is the main focus for Precision Medicine. Radiolabeled ligands can be used as predictive biomarkers which can confirm target expression by cancers using positron emission tomography (PET). The same ligand can subsequently be labeled with a therapeutic radionuclide for targeted radionuclide therapy. This combined approach is termed “Theranostics”. The prostate-specific membrane antigen (PSMA) has emerged as an attractive diagnostic and therapeutic target for small molecule ligands in prostate cancer. It can be labeled with either positron emitters for PET-based imaging or beta and alpha emitters for targeted radionuclide therapy. This review article summarizes the important concepts for Precision Medicine contributing to improved diagnosis and targeted therapy of patients with prostate cancer and we identify some key learning points and areas for further research.

Focal PSMA-Positive Pleural Lesion in a Patient With Stage II Prostate Carcinoma

ABSTRACT

A 70-year-old man with histopathologically proven prostate carcinoma (Gleason, 5 + 5; prostate-specific antigen level, 6.2 μg/mL) was referred for an 18F-PSMA-1007 PET/CT scan. The scan revealed bilateral PSMA uptake in the prostate, representing the primary tumor, but no evidence of PSMA-positive lymph nodes. However, a left-sided ventral pleural thickening showed focal PSMA uptake. Lesion biopsy showed no signs of malignancy, and prostatectomy was performed. The 1-year follow-up CT thorax showed growth of approximately 20% of the pleural lesion. Subsequently, video-assisted thoracic surgery of the lesion was performed. Histopathology showed a solitary fibrous tumor, a rare mesenchymal tumor.

Spurious Uptake on 68Ga-Prostate-Specific Membrane Antigen PET/CT Due to Ankylosing Spondylitis; A Rare Pitfall in Imaging of Biochemical Recurrence of Prostate Cancer

ABSTRACT

Bone is one of the most common sites of prostate cancer recurrence, and 68Ga-prostate-specific membrane antigen (PSMA) uptake by benign bone entities poses a diagnostic dilemma. We describe the case of a 60-year-old man with recurrence in a small presacral node on 68Ga-PSMA PET/CT. Of note, the images also demonstrated bilateral asymmetrical sacroiliac joint uptake. A history of ankylosing spondylitis was subsequently elicited, confirming the radiographic suspicion of sacroiliitis, therefore confirming the nonmalignant nature of 68Ga-PSMA uptake related to sacroiliitis rather than osseous recurrence from prostate carcinoma. 68Ga-PSMA uptake may indicate angioneogenesis in sacroiliitis and consequently may be helpful in assessing disease activity and therapy response.

68Ga-PSMA-HBED-CC PET/CT Findings in a Patient of Polyostotic Fibrous Dysplasia

ABSTRACT

A 43-year-old man diagnosed with fibrous dysplasia with McCune-Albright syndrome was subjected to 18F-fluoride bone scan and 68Ga-PSMA-HBED-CC PET/CT as per the institution protocol. 18F-bone scan revealed extensive involvement of axial and appendicular skeleton confirming polyostotic fibrous dysplasia. 68Ga-PSMA PET/CT showed increased tracer uptake in corresponding lesions of fibrous dysplasia. PSMA uptake in fibrous dysplasia lesions has been rarely described with literature evidence being limited to anecdotal case reports. Nevertheless, due to increasing use of PSMA PET/CT, one should be aware of this false-positive finding to avoid misinterpretation of the scans.

Focal unspecific bone uptake on [18F]-PSMA-1007 PET: a multicenter retrospective evaluation of the distribution, frequency, and quantitative parameters of a potential pitfall in prostate cancer imaging

Purpose

Improved logistics and availability led to a rapid increase in the use of [¹⁸F]-PSMA-1007 for prostate cancer PET imaging. Initial data suggests increased uptake in benign lesions compared to [⁶⁸ Ga]-PSMA-11, and clinical observations found increased unspecific bone uptake (UBU). We therefore investigate the frequency and characteristics of UBU in [¹⁸F]-PSMA-1007 PET.

Methods

We retrospectively analyzed [¹⁸F]-PSMA-1007 PET scans from four centers for the presence of UBU, defined as a focal mild-to-moderate uptake (SUV_max < 10.0) not obviously related to a benign or malignant cause. If present, up to three leading UBUs were quantified (SUV_max), localized, and correlated to clinical parameters, such as age, PSA, injected dose, Gleason score, tumor size (T1–T4), and type of PET scanner (analog vs. digital). Additionally, clinical and imaging follow-up results and therapeutic impact were evaluated.

Results

UBUs were identified in 179 out of 348 patients (51.4%). The most frequent localizations were ribs (57.5%) and pelvis (24.8%). The frequency of UBUs was not associated with PSA, Gleason score, tumor size, age, or the injected [¹⁸F]-PSMA-1007 dose. UBUs were significantly more frequent in images obtained with digital PET/CT scans (n = 74, 82%) than analog PET/CT scans (n = 221, 40.3%) (p = .0001) but not in digital PET/MR (n = 53, 51%) (p = .1599). In 80 out of 179 patients (44.7%), the interpretation of UBUs was critical for therapeutic management and therefore considered clinically relevant. For 65 UBUs, follow-ups were available: three biopsies, three radiotherapies with PSA follow-up, and 59 cases with imaging. After follow-up, UBUs were still considered unclear in 28 of 65 patients (43%), benign in 28 (43%), and malignant in nine (14%) patients.

Conclusion

UBUs occur in two-thirds of patients imaged with [¹⁸F]-PSMA-1007 PET/CT and are significantly more frequent on digital PET scanners than analog scanners. UBUs should be interpreted carefully to avoid over-staging.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-021-05424-x.

Does Prostate-Specific Membrane Antigen Avidity of Vertebral Hemangioma Change?

ABSTRACT

Vertebral hemangiomas are the most common benign tumors of the spine and mostly occur in the thoracic spine. Mostly they are detected incidentally during imaging studies for other reasons. We present the case of vertebral hemangioma that showed prostate-specific membrane antigen uptake in the second 68Ga-prostate-specific membrane antigen PET/CT, whereas no uptake was observed in the initial study.

68Ga-Prostate-Specific Membrane Antigen PET-Positive Paget Bone Disease With Metastatic Prostatic Carcinoma

Paget bone disease is a chronic benign bone disease characterized by excessive and abnormal bone remodeling. The scintigraphic and bone SPECT/CT hybrid imaging appearances of the affected bone(s) depend on the stage of the disease. We report the case of a patient newly diagnosed with prostate cancer who was found to have multiple osseous metastases, with coexisting Paget disease in the left hemipelvis diagnosed because of typical scintigraphic and SPECT/CT appearance. Ga-prostate-specific membrane antigen PET/CT was also performed for initial staging. Pagetoid bones showed increased prostate-specific membrane antigen uptake like skeletal metastases.

Impact of 68Ga-PSMA PET/CT in the treatment of prostate cancer: Initial experience in Spain

Aim

To evaluate whether positron-emission tomography/computed tomography with ⁶⁸Ga-PSMA (⁶⁸Ga-PSMA PET/CT) influences the therapeutic management of patients with primary or recurrent prostate cancer (PCa).

Background

Although ⁶⁸Ga-PSMA PET/CT is one of the best options for staging or restaging patients with PCa, its availability is still very limited in Spain. The present study reports the results of the first group of patients in Spain who underwent ⁶⁸Ga-PSMA PET/CT imaging.

Materials and methods

All patients (n = 27) with a histological diagnosis of PCa who underwent ⁶⁸Ga-PSMA PET/CT prior to the definitive treatment decision at the only centre with this technology in Spain during 2017-2018 were included. Two nuclear medicine physicians and a radiologist reviewed the imaging studies. The clinical impact was assessed from a theoretical perspective, based on the treatment that would have been applied if no data from the ⁶⁸Ga-PSMA PET/CT were available.

Results

Most patients (n = 26; 96%) had persistent disease or biochemical recurrence after radical prostatectomy, radiotherapy, or combined treatment. One patient underwent ⁶⁸Ga-PSMA PET/CT imaging to stage high-risk PCa. Overall, ⁶⁸Ga-PSMA PET/CT was positive in 19 patients (70.4%). In 68.75% of these patients, none of the other imaging tests-MRI, CT, or bone scans-performed prior to the ⁶⁸Ga-PSMA PET/CT were able to detect the presence of cancerous lesions. Overall, the findings of the ⁶⁸Ga-PSMA PET/CT led to a modification of the therapeutic approach in 62.96% of the patients in the study.

Conclusions

⁶⁸Ga-PSMA PET/CT alters the therapeutic approach in a substantial proportion of patients with PCa.

Added value of 68Ga-PSMA PET/CT for the detection of bone metastases in patients with newly diagnosed prostate cancer and a previous 99mTc bone scintigraphy

Purpose

To investigate the added value and diagnostic accuracy of ⁶⁸Ga-PSMA PET/CT versus bone scintigraphy (BS) for bone metastasis detection at the primary staging of prostate cancer (PCa).

Methods

Inclusion criteria involved consecutive patients with newly diagnosed intermediate- to high-risk PCa, who had undergone BS, mostly with supplementary SPECT/low-dose CT, and ⁶⁸Ga-PSMA-11 PET/CT within less than 3 months without therapy initiation between the two investigations. BS was evaluated according to clinical routine and reported as no bone metastases (M0), bone metastases (M1), or equivocal (Me). The ⁶⁸Ga-PSMA-11 PET/CT was blindly evaluated by three specialists as M0, M1, or Me at the patient level. Sensitivity analyses were conducted using a “best valuable comparator” using all available imaging and clinical follow-up as a reference.

Results

In total, 112 patients were included; ⁶⁸Ga-PSMA-11 PET/CT showed a sensitivity of 1.00, specificity of 0.93–0.96, positive predictive value of 0.74–0.81, and negative predictive value of 1.00. ⁶⁸Ga-PSMA-11 PET/CT revealed bone metastases in 8 of 81 patients with M0 disease according to BS. ⁶⁸Ga-PSMA-11 PET/CT confirmed the presence of bone metastases in all patients (n = 9) with M1 disease according to BS. In patients with Me by BS, ⁶⁸Ga-PSMA PET/CT provided a definite result in 20 of 22 patients. ⁶⁸Ga-PSMA-11 PET/CT resulted in a false-positive answer in four patients with solitary rib lesions.

Conclusion

⁶⁸Ga-PSMA-11 PET/CT revealed bone metastases in 10% of patients without bone metastases on BS and in 36% patients with indeterminate BS. However, solitary PSMA-avid lesions in the ribs should be interpreted cautiously as they may represent false-positive findings.