68Ga-PSMA Uptake in Neurofibromas Demonstrated on PET/CT in a Patient With Neurofibromatosis Type 1

Prostate-Specific Membrane Antigen-Avid Neurofibroma Mimicking Cutaneous Metastasis in Metastatic Castration-Resistant Prostate Cancer on 18 F-PSMA-1007 PET/CT

ABSTRACT

The occurrence of cutaneous metastases in prostate cancer is exceedingly rare. Many benign lesions and nonprostatic cancers can express the prostate-specific membrane antigen (PSMA). They can potentially mimic metastasis of prostate cancer and lead to misinterpretation of PSMA PET/CT findings. Additionally, it has significant management and prognostic implications. We present a rare case of an 88-year-old man with metastatic castration-resistant prostate cancer who showed a PSMA-expressing subcutaneous nodule in the scalp on 18 F-PSMA-1007 PET/CT, raising the suspicion of cutaneous metastasis. However, its biopsy revealed a neurofibroma, altering the disease prognosis and management.

A Case Series Depicting PSMA Expression in Nonmalignant Lesions

Prostate-specific membrane antigen (PSMA) is a widely accepted and used tracer in staging and biochemical recurrences of prostate cancer. PSMA is extensively expressed in normal prostatic epithelial cells and prostate cancer cells, with some amount of expression also in nonprostatic cells. False-positive PSMA uptake in nonmalignant lesions creates ambiguity in disease detection. In such cases, histopathological correlation and radiological follow-up assist in clinical decision-making. In this case series, we illustrate a few cases where PSMA uptake was incidentally found in some of the commonly occurring benign conditions.

Intense 68 Ga-PSMA Uptake in Neurofibroma Mimicking Cutaneous Metastases in a Patient With Prostate Cancer

ABSTRACT

Prostate cancer is the most common cancer in men. 68 Ga-PSMA PET/CT is frequently used in staging and restaging prostate cancer; it is important to keep in mind the causes of false-positives when evaluating imaging. We present findings of 68 Ga-PSMA PET/CT and histopathological features of a 68-year-old prostate cancer man with neurofibroma. 68 Ga-PSMA PET/CT showed intense 68 Ga-PSMA uptake in neurofibroma.

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.

Image-Based Differentiation of Benign and Malignant Peripheral Nerve Sheath Tumors in Neurofibromatosis Type 1

Neurofibromatosis type 1 (NF1) is a dominant hereditary disease characterized by the mutation of the NF1 gene, affecting 1/3000 individuals worldwide. Most NF1 patients are predisposed to benign peripheral nerve sheath tumors (PNSTs), including cutaneous neurofibromas (CNFs) and plexiform neurofibromas (PNFs). However, 5%-10% of PNFs will ultimately develop into malignant peripheral nerve sheath tumors (MPNSTs), which have a poor prognosis. Early and reliable differentiation of benign and malignant tumors in NF1 patients is of great necessity. Pathological evaluation is the “gold standard” for a definite diagnosis, but the invasive nature of the biopsy procedure restricts it from applying as a screening tool during the decades-long follow-up of these patients. Non-invasive image-based diagnostic methods such as CT and MRI are often considered essential screening tools for multiple types of tumors. For NF1 patients’ lifelong regular follow-ups, these radiological methods are currently used for tumor evaluation. However, no consensus was established on screening the malignant transformation of benign PNSTs. Moreover, novel technologies like radiogenomics and PET-MRI have not been well evaluated and fully adopted for NF1 patients. This review summarizes current studies of different imaging methods for differentiating benign and malignant tumors in NF1. Meanwhile, we discussed the prospects of the usage of new tools such as radiogenomics and PET-MRI to distinguish MPNST from benign PNSTs more precisely. Summarizing these findings will help clarify the directions of future studies in this area and ultimately contribute to the radiology images-based clinical screening of MPNST in NF1 patients and finally improve the overall survival rates of these patients.

The differential diagnostic value of dual-phase 18F-DCFPyL PET/CT in prostate carcinoma

OBJECTIVE

Binding of ¹⁸F-DCFPyL at prostate cancer (PC) cells increases over time. The dual-phase protocol may be helpful in separating benign lesions from malignant ones associated with prostate cancer. The purpose of this study was to retrospectively analyze the incremental diagnostic value of ¹⁸F-DCFPyL dual-time imaging in patients with prostate cancer.

METHOD

114 prostate-related malignant lesions and 43 benign lesions in 38 patients with prostate cancer were retrospectively analyzed. Maximum standardized uptake value (SUVmax) for benign and prostate-related malignant lesions were calculated at min 60 and min 120 of PET/CT imaging. In order to calculate SUV ratio, the SUVmax of left gluteus maximus was measured at the same time. The difference of SUVmax metrics and SUV ratio between malignant and benign lesions was statistically analyzed, the cut-off value of ROC curve was calculated, and the diagnostic efficacy of SUVmax index and SUV ratio at two time points was compared.

RESULTS

SUVmax metrics and SUV ratio of early and delayed imaging of PC-related malignant lesions were significantly higher than those of benign lesions (p < 0.05). In terms of individual indicators, the highest accuracy and sensitivity was in the delayed SUV ratio (89.2% and 94.7%), the best specificity was in the early SUVmax (93.0%). When the individual and combined indicators were compared together, the SUV ratio in the delay period still showed the best diagnostic sensitivity and accuracy, and the best specificity were SUVmax early and ▵SUVmax, SUVmax early and RI.

CONCLUSIONS

Uptake of ¹⁸F-DCFPyL increased over time in prostate-associated malignant lesions compared with benign tissue. For single-phase imaging, 2-hour (delayed) imaging has better diagnostic performance. However, the dual-phase imaging (1 and 2 h) are helpful in the differential diagnosis of prostate-associated malignant lesions and benign lesions.

PET/CT variants and pitfalls in prostate cancer: What you might see on PET and should never forget

2-deoxy-2-[¹⁸F]fluorodeoxyglucose (FDG) positron emission tomography (PET) gained an impressive role in the diagnostic management of many oncological diseases, even though its use in imaging prostate cancer (PC) is limited to selected cases, mostly advanced stage of PC and selection for prostate specific antigen membrane (PSMA) radioligand therapy (RLT). In the past years, several PET tracers have been developed for both staging and restaging PC. The three most employed PET molecules in daily practice are [¹¹C] or [¹⁸F]F-Choline, [¹⁸F]F-Fluciclovine (Anti-1- amino-3-[18F]Fluorocyclobutane-1-Carboxylic Acid, also known as (Anti-[¹⁸F]FACBC), [⁶⁸Ga]Ga-PSMA and recently FDA approved the first Fluorinated PSMA-based named [¹⁸F]F-DCFPyl. Each one has its own physiological and peculiarity which are worth exploring. Moreover, an increasing number of case reports and studies have reported tracers' variants, pitfalls, or even non-prostatic diseases (benign and malignant) incidentally detected. In prostate oncology, PET can be performed with several indications in different stages of disease, as highlighted in the EAU Guidelines on PC. A correct scan interpretation depends on the knowledge of both the physiological distribution of the tracers and the uptake of possible variants and pitfalls. The aim of this critical review is to provide a comprehensive knowledge of physiological distribution of these three tracers, as well as an updated overview of variants and pitfalls.

Increased Prostate-Specific Membrane Antigen Uptake in Neurofibromatosis

A 51-year-old man with 30-year neurofibromatosis and 2-month elevated prostate-specific antigen and back pain underwent a Ga-prostate-specific membrane antigen (PSMA) PET/CT scan for possible prostate cancer. Prostate-specific membrane antigen PET/CT imaging showed no abnormal uptake of the prostate. However, in addition to PSMA uptake in his left lung, thorax, and right ilium, which was confirmed being a lung squamous cell carcinoma by a lung biopsy, widespread uptake was also observed in his skin fibroma lesions. This case demonstrates that benign neurofibromatosis could have uptake of PSMA.

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.