Imaging of a Thymoma Incidentally Detected by C-11 Choline PET/CT

Prostate Cancer-PET Imaging Update

Prostate cancer is the most common non-dermatologic cancer in men, and one of the leading causes of cancer-related mortality. The incidence of prostate cancer increases precipitously after the age of 65 and demonstrates variable aggressiveness, depending on its grade and stage at diagnosis. Despite recent advancements in prostate cancer treatment, recurrence is seen in 25% of patients. Advancements in prostate cancer Positron Emission Tomography (PET) molecular imaging and recent United States Food and Drug Administration (FDA) approvals have led to several new options for evaluating prostate cancer. This manuscript will review the commonly used molecular imaging agents, with an emphasis on Fluorine-18 fluciclovine (Axumin) and PSMA-ligand agents, including their protocols, imaging interpretation, and pitfalls.

Incidental Uptake of 18F-Fluciclovine by Type AB Thymoma

ABSTRACT

Biochemical recurrence of prostate cancer, detected by a rising PSA, may reflect intraprostatic or extraprostatic recurrence. 18F-Fluciclovine (Axumin), a synthetic amino acid substrate in tumor metabolism, has frequently been used for to localize recurrent prostate cancers. We present a 71-year-old man with biochemical recurrence of prostate cancer but no convincing imaging findings on 18F-fluciclovine PET/CT. Of note, however, was an incidental uptake within the anterior mediastinum, which was found on biopsy to be a type AB thymoma. With this, we stress that awareness of false-positive uptake patterns is crucial for accurate diagnosis of recurrent prostate cancer.

Current Roles of PET/CT in Thymic Epithelial Tumours: Which Evidences and Which Prospects? A Pictorial Review

Simple Summary

Thymic epithelial tumours are uncommon malignancies. Histologically, they may be distinguished in different subtypes and different relapse risk classes. Surgery, sometimes after induction therapy, stays the best treatment option, and long-term results depend on the disease stage and completeness of resection. In this context, ¹⁸F FDG PET CT scan has been reported to play different roles in the care strategy of thymic epithelial tumours. In the present review, we analyse current evidences, the use of this imaging tool and future application prospects.

Abstract

Background: The use of ¹⁸F FDG PET/CT scan in thymic epithelial tumours (TET) has been reported in the last two decades, but its application in different clinical settings has not been clearly defined. Methods: We performed a pictorial review of pertinent literature to describe different roles and applications of this imaging tool to manage TET patients. Finally, we summarized future prospects and potential innovative applications of PET in these neoplasms. Results: ¹⁸FFDG PET/CT scan may be of help to distinguish thymic hyperplasia from thymic epithelial tumours but evidences are almost weak. On the contrary, this imaging tool seems to be very performant to predict the grade of malignancy, to a lesser extent pathological response after induction therapy, Masaoka Koga stage of disease and long-term prognosis. Several other radiotracers have some application in TETs but results are limited and almost controversial. Finally, the future of PET/CT and theranostics in TETs is still to be defined but more detailed analysis of metabolic data (such as texture analysis applied on thymic neoplasms), along with promising preclinical and clinical results from new “stromal PET tracers”, leave us an increasingly optimistic outlook. Conclusions: PET plays different roles in the management of thymic epithelial tumours, and its applications may be of help for physicians in different clinical settings.

4-11C-Methoxy N-(2-Diethylaminoethyl) Benzamide: A Novel Probe to Selectively Target Melanoma

We report the synthesis and preclinical evaluation of a ¹¹C-labeled probe to target melanoma using PET. Methods: The target compound 4-¹¹C-methoxy N-(2-diethylaminoethyl) benzamide (4-¹¹C-MBZA) was prepared via the ¹¹C-methylation of 4-hydroxy N-(2-diethylaminoethyl) benzamide (4-HBZA). The in vitro binding was performed using B16F1 (melanoma cells), MCF-10A (breast epithelial cells), and MDA-MB 231 (breast cancer cells). The internalization studies were conducted using B16F1 cells. In vivo biodistribution and small-animal PET imaging were performed in mice bearing B16F1 melanoma tumor xenografts. Results: The target compound 4-¹¹C-MBZA was prepared in 46% ± 7% radiochemical yields by reacting ¹¹C-methyltriflate with 4-HBZA followed by high-performance liquid chromatography purification. The specific activity of this compound was 853 ± 29.6 GBq/μmol (23 ± 0.8 Ci/μmol). The binding of 4-¹¹C-MBZA to B16F1, MCF-10A, and MDA-MB-231 cells was 6.41% ± 1.28%, 1.51% ± 0.17%, and 0.30% ± 0.17%, respectively. Internalization studies using B16F1 melanoma cells show 60.7% of the cell-bound activity was internalized. Results from biodistribution studies show a rapid and high uptake of radioactivity in the tumor, with uptake levels reaching 5.85 ± 0.79 and 8.13 ± 1.46 percentage injected dose per gram at 10 and 60 min, respectively. Low uptake in normal tissues in conjunction with high tumor uptake resulted in high tumor-to-tissue ratios. On small-animal PET images, the tumor was clearly delineated soon after 4-¹¹C-MBZA injection and tumor uptake reached 4.2 percentage injected dose per gram by 20 min. These preclinical evaluations show a high propensity of 4-¹¹C-MBZA toward melanoma tumor. Conclusion: We successfully developed 4-¹¹C-MBZA as a PET imaging probe, displaying properties advantageous over those for its ¹⁸F analogs. These preclinical evaluation results demonstrate the clinical potential of this probe to selectively target melanoma.

¹¹C-Choline PET/CT in Recurrent Prostate Cancer and Nonprostatic Neoplastic Processes

Choline positron emission tomography (PET)/computed tomography (CT), with both carbon 11 ((11)C) choline and fluorine 18 ((18)F) choline, is an increasingly used tool in the evaluation of patients with biochemically recurrent prostate cancer. It has allowed detection and localization of locally recurrent and metastatic lesions that were difficult or impossible to identify using more conventional modalities. Many of the patients followed for their prostate cancer are elderly and have a higher rate of nonprostate cancer lesions or malignancies. As our experience with choline PET/CT has grown, it has become apparent that many of these nonprostate cancer processes, both benign and malignant, can be detected. Invasive thymoma, renal cell carcinoma, papillary thyroid carcinoma, and parathyroid adenoma are a few of the processes that have been incidentally detected with (11)C-choline PET/CT at our institution and have significantly altered subsequent clinical management of the patient. Although most of the secondary lesions are detected due to their increased (11)C-choline avidity, several have been detected due to their decreased or lack of avidity in the background of a highly avid organ. For instance, large liver masses that are relatively non-choline-avid create large activity defects in the otherwise highly active liver. Familiarity with normal (11)C-choline physiologic activity, the most common prostate metastatic patterns, and imaging characteristics of secondary lesions is essential for the detection and correct diagnosis of such lesions so that proper follow-up and management can be recommended.

Squamous cell carcinoma of the tonsil incidentally detected by 18F-choline PET/CT

We report a case of squamous cell carcinoma of the tonsil incidentally detected by F-choline PET/CT. A 55-year-old male patient with a history of prostate cancer underwent F-choline PET/CT for restaging. PET/CT revealed a focal area of increased F-choline uptake corresponding to the left tonsil. No other areas of abnormal F-choline uptake were detected in the rest of the body. Based on these PET/CT findings, the patient underwent clinical examination and biopsy of the left tonsil. Histology demonstrated the presence of a squamous cell carcinoma of the tonsil.

Colorectal carcinoma with bone metastases detected by 18F-choline PET/CT

We report a case of metastatic colorectal carcinoma detected by F-choline PET/CT. A 72-year-old man with history of prostate cancer (previously treated with prostatectomy) underwent F-choline PET/CT for restaging. PET/CT revealed a focal area of increased F-choline uptake corresponding to a rectal nodule. Furthermore, 2 areas of increased radiopharmaceutical uptake were evident in the right clavicle and in the body of the 10th dorsal vertebra, corresponding to the osteolytic lesions. Based on these PET/CT findings, the patient underwent biopsy of the rectal nodule and left clavicular lesion. Histologic examination demonstrated the presence of a colorectal carcinoma metastatic to the bone.

Evaluation of thymic tumors with 18F-FDG PET-CT: a pictorial review

Thymic tumors represent a broad spectrum of neoplastic disorders and pose considerable diagnostic difficulties. A non-invasive imaging study to determine the nature of thymic lesions can have significant impact on management of such tumors. 18F-flurorodeoxyglucose (18F-FDG) positron emission tomography-computed tomography (PET-CT) has shown promising results in characterization of thymic tumors. The objective of this article is to provide an illustrative tutorial highlighting the clinical utility of 18F-FDG PET-CT imaging in patients with thymic tumors. We have pictorially depicted the 18F-FDG PET-CT salient imaging characteristics of various thymic tumors, both epithelial and non-epithelial. Also discussed is the dynamic physiology of thymus gland which is to be kept in mind when evaluating thymic pathology on 18F-FDG PET-CT, as it can lead to interpretative pitfalls.

Imaging Comparison between18F-FDG-PET/CT and18F-Flouroethyl Choline PET/CT in Rare Case of Thymus Carcinoma Exhibiting a Positive Choline Uptake

It is of great value by using PET imaging in oncology to recognize any atypical uptake not related to the underlying disease. That helps in avoiding the false positive finding and may contribute in extending the application range of used radiopharmaceuticals in further disorders. It is well known that radiolabeled choline is an essential PET tracer used currently in prostate cancer. The physiological choline distribution was described. Nevertheless there is still a lack of studies, which describe this distribution in young patients; given that the radiolabeled choline is generally being used in the field of prostate cancer. Whether the thymus exhibits normally a positive choline uptake or not is still unknown. In particular, it is known that the lymphocytes express high affinity of choline transporter and enzymes involving its metabolism. Some cases of thymus carcinoma exhibiting a positive choline had been reported in the literature, however, mostly using ¹¹C-choline. We report a rare case of metastatic thymic carcinoma detected incidentally using ¹⁸F-choline-PET in a 78-year-old male patient referred with elevation of prostate specific antigen. Moreover we present a comparison pattern with ¹⁸F-FDG-PET modality, in which ¹⁸F-choline-PET was turned out to be superior in tumor delineation.