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Purpose: Radiolabelled fibroblast activation protein inhibitors (FAPIs) are becoming increasingly important for imaging various tumour diseases. However, it is essential to be aware of potential pitfalls. Here, we investigate FAP expression in the thyroid gland in autoimmune thyroiditis (AIT). Methods: AIT patients with pathological thyroid uptake on [68Ga]Ga-FAPI PET were compared with glucose metabolism on 2-[18F]FDG PET in terms of SUVmax/SUVpeak/SUVmean/tissue-to-background ratio (TBR), and with a healthy control group. Results: Between September 2019 and July 2021, 6 patients presented with a visually increased thyroid uptake and TBR on [68Ga]Ga-FAPI PET. In the retrospective clinical work-up, all patients had known or newly diagnosed AIT. Compared to a matched healthy control group, FAP expression and glucose metabolism were significantly increased ([68Ga]Ga-FAPI (SUVpeak): 7.0 vs. 1.7; p = 0.004/(TBRbloodpool): 6.8 vs. 1.7; p = 0.002; 2-[18F]FDG (SUVpeak): 3.9 vs. 1.4; p = 0.004/(TBRbloodpool): 4.0 vs. 1.2; p = 0.041). However, there was no significant difference in median uptake between [68Ga]Ga-FAPI and 2-[18F]FDG PET (SUVpeak: 7.3 vs. 5.6; p = 0.104). Conclusion: Patients with AIT show higher thyroid uptake on [68Ga]Ga-FAPI and 2-[18F]FDG PET. Incidental thyroid uptake is another pitfall in the interpretation of [68Ga]Ga-FAPI PET and should prompt a clinical work-up. [ABSTRACT FROM AUTHOR]

Introduction: Primary cardiac paragangliomas are rare tumors. Metastatic disease is even rarer. Surgical management is technically challenging, and sometimes even impossible. Available therapeutic modalities for metastatic disease include external beam radiation therapy as well as systemic treatments, namely 131I-MIBG and more recently, peptide receptor radionuclide therapy (PRRT) with 177Lu-DOTATATE. To our knowledge, this is the first case of progressive unresectable cardiac paraganglioma with intracardiac extension treated with dosimetry based personalized PRRT to be reported. This case is of particular interest since it documents for the first time the efficacy, and especially the safety of the 177Lu-DOTATATE PRRT in this precarious context for which therapeutic options are limited. Case Presentation: A 47-year-old man with no medical history consulted for rapidly decreasing exercise tolerance. The investigation demonstrated an unresectable progressing metastatic cardiac paraganglioma with intracardiac extension. The patient was treated with personalized 177Lu-DOTATATE PRRT and showed complete symptomatic and partial anatomical responses, with a progression-free survival of 13 months. Conclusions: PRRT with 177Lu-DOTATATE should be considered for inoperable cardiac paraganglioma. No major hemodynamic complications were experienced. Therapy resulted in safety and substantially improved quality of life. [ABSTRACT FROM AUTHOR]

Purpose: Radiolabelled fibroblast activation protein inhibitors (FAPIs) are becoming increasingly important for imaging various tumour diseases. However, it is essential to be aware of potential pitfalls. Here, we investigate FAP expression in the thyroid gland in autoimmune thyroiditis (AIT)., Methods: AIT patients with pathological thyroid uptake on [ 68 Ga]Ga-FAPI PET were compared with glucose metabolism on 2-[ 18 F]FDG PET in terms of SUV max /SUV peak /SUV mean /tissue-to-background ratio (TBR), and with a healthy control group., Results: Between September 2019 and July 2021, 6 patients presented with a visually increased thyroid uptake and TBR on [ 68 Ga]Ga-FAPI PET. In the retrospective clinical work-up, all patients had known or newly diagnosed AIT. Compared to a matched healthy control group, FAP expression and glucose metabolism were significantly increased ([ 68 Ga]Ga-FAPI (SUV peak ): 7.0 vs. 1.7; p = 0.004/(TBR bloodpool ): 6.8 vs. 1.7; p = 0.002; 2-[ 18 F]FDG (SUV peak ): 3.9 vs. 1.4; p = 0.004/(TBR bloodpool ): 4.0 vs. 1.2; p = 0.041). However, there was no significant difference in median uptake between [ 68 Ga]Ga-FAPI and 2-[18F]FDG PET (SUV peak : 7.3 vs. 5.6; p = 0.104)., Conclusion: Patients with AIT show higher thyroid uptake on [ 68 Ga]Ga-FAPI and 2-[ 18 F]FDG PET. Incidental thyroid uptake is another pitfall in the interpretation of [ 68 Ga]Ga-FAPI PET and should prompt a clinical work-up., (© 2024. The Author(s).)

Prospective results have demonstrated favorable safety and efficacy of [ 177 Lu]Lu-PSMA radiopharmaceutical therapy for up to 6 cycles in men with metastatic castration-resistant prostate cancer. However, no systematic data are available outlining the feasibility of extended therapy beyond 6 cycles. We aim to evaluate the safety and efficacy of extended [ 177 Lu]Lu-PSMA radiopharmaceutical therapy in patients who have received more than 6 cycles. Methods: In total, 111 patients were included in this multicenter retrospective analysis. Based on individual decisions, patients underwent uninterrupted continuation of therapy (continuous treatment) or reexposure after a therapy break (rechallenge treatment) between 2014 and 2023. Overall survival, 50% prostate-specific antigen (PSA) decline (measured 8-12 wk after treatment initiation or rechallenge), PSMA PET response, and grades per Common Terminology Criteria for Adverse Events were assessed. χ 2 tests, multivariable Cox regression analysis, and log-rank tests were applied for statistical analyses. Results: Patients received extended treatment with [ 177 Lu]Lu-PSMA, either as a continuous treatment (43/111, 38.7%) or as a rechallenge (68/111, 61.3%) treatment, with median cumulative doses of 57.4 or 60.8 GBq, respectively. Overall survival from the initiation of [ 177 Lu]Lu-PSMA was 31.3, 23.2, and 40.2 mo for the entire cohort, the continuous treatment group, and the rechallenge treatment group, respectively. The initial 50% PSA decline was significantly higher in the retreated group than in the continuous group (57/63 [90.4%] vs. 26/42 [61.9%]; P = 0.006). A 50% PSA decline was observed in 23 of 62 patients (37.1%) after the first rechallenge. The rate of grades 3-4 toxicity was comparable between continuous and rechallenge treatments (anemia, 7/43 [16.3%] vs. 13/68 [19.1%)], P = 0.6; leukocytopenia, 1/43 [2.3%] vs. 2/67 [3.0%], P = 0.3; thrombocytopenia, 3/43 [7.0%] vs. 3/68 [4.4%], P = 0.3; renal, 2/43 [4.7%] vs. 5/68 [7.4%], P = 0.2). Conclusion: Extended therapy with [ 177 Lu]Lu-PSMA is safe and has not been associated with increased grades 3-4 toxicity. Patient candidates for extended treatment experienced a favorable median survival of 31.3 mo from the first administration. Response under [ 177 Lu]Lu-PSMA rechallenge demonstrated preserved efficacy of [ 177 Lu]Lu-PSMA after a treatment break., (© 2024 by the Society of Nuclear Medicine and Molecular Imaging.)

Fibroblast activation protein-α (FAP) is often highly expressed by sarcoma cells and by sarcoma-associated fibroblasts in the tumor microenvironment. This makes it a promising target for imaging and therapy. The level of FAP expression and the diagnostic value of 68 Ga-FAP inhibitor (FAPI) PET for sarcoma subtypes are unknown. We assessed the diagnostic performance and accuracy of 68 Ga-FAPI PET in various bone and soft-tissue sarcomas. Potential eligibility for FAP-targeted radiopharmaceutical therapy (FAP-RPT) was evaluated. Methods: This prospective observational trial enrolled 200 patients with bone and soft-tissue sarcoma who underwent 68 Ga-FAPI PET/CT and 18 F-FDG PET/CT (186/200, or 93%) for staging or restaging. The number of lesions detected and the uptake (SUV max ) of the primary tumor, lymph nodes, and visceral and bone metastases were analyzed. The Wilcoxon test was used for semiquantitative assessment. The association of 68 Ga-FAPI uptake intensity, histopathologic grade, and FAP expression in sarcoma biopsy samples was analyzed using Spearman r correlation. The impact of 68 Ga-FAPI PET on clinical management was investigated using questionnaires before and after PET/CT. Eligibility for FAP-RPT was defined by an SUV max greater than 10 for all tumor regions. Results: 68 Ga-FAPI uptake was heterogeneous among sarcoma subtypes. The 3 sarcoma entities with the highest uptake (mean SUV max ± SD) were solitary fibrous tumor (24.7 ± 11.9), undifferentiated pleomorphic sarcoma (18.8 ± 13.1), and leiomyosarcoma (15.2 ± 10.2). Uptake of 68 Ga-FAPI versus 18 F-FDG was significantly higher in low-grade sarcomas (10.4 ± 8.5 vs. 7.0 ± 4.5, P = 0.01) and in potentially malignant intermediate or unpredictable sarcomas without a World Health Organization grade (not applicable [NA]; 22.3 ± 12.5 vs. 8.5 ± 10.0, P = 0.0004), including solitary fibrous tumor. The accuracy, as well as the detection rates, of 68 Ga-FAPI was higher than that of 18 F-FDG in low-grade sarcomas (accuracy, 92.2 vs. 80.0) and NA sarcomas (accuracy, 96.9 vs. 81.9). 68 Ga-FAPI uptake and the histopathologic FAP expression score ( n = 89) were moderately correlated (Spearman r = 0.43, P < 0.0002). Of 138 patients, 62 (45%) with metastatic sarcoma were eligible for FAP-RPT. Conclusion: In patients with low-grade and NA sarcomas, 68 Ga-FAPI PET demonstrates uptake, detection rates, and accuracy superior to those of 18 F-FDG PET. 68 Ga-FAPI PET criteria identified eligibility for FAP-RPT in about half of sarcoma patients., (© 2024 by the Society of Nuclear Medicine and Molecular Imaging.)

Musculoskeletal disorders of nononcological origin are one of the most frequent reasons for consultation. Patients suffering from musculoskeletal disorders also consult more than once for the same reason. This results in multiple clinical follow-ups after several radiological and serum examinations, the main ones including X-rays targeting the painful anatomical region and inflammatory serum parameters. As part of their work up, patients suffering from musculoskeletal disorders often require multisequence, multi-parameter MRI. PET/MRI is a promising imaging modality for their diagnosis, with the added advantage of being able to be performed in a single visit. PET/MRI is particularly useful for diagnosing osteomyelitis, spondylodiscitis, arthritis, many pediatric pathologies, and a wide range of other musculoskeletal pathologies. PET/MRI is already used to diagnose malignant bone tumors such as osteosarcoma. However, current knowledge of the indications for PET/MRI in nononcological musculoskeletal disorders is based on studies involving only a few patients. This review focuses on the usefulness of PET/MRI for diagnosing nononcological musculoskeletal disorders., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Tugce Telli reports a relationship with ABX GmbH that includes: speaking and lecture fees. Robert Seifert reports a relationship with Böhringer Ingelheim Fonds and Else Köner-Fresenius-Stiftung that includes: funding grants. Wolfgang P. Fendler reports a relationship with Janssen Pharmaceuticals Inc, Calyx Chemicals and Pharmaceuticals Ltd, Novartis Pharmaceuticals Corporation, Telix Pharmaceuticals Limited, GE Healthcare, Eczacibasi Pharmaceuticals Marketing, ABX GmbH, and Amgen Inc that includes: consulting or advisory, funding grants, and speaking and lecture fees. Federico Caobelli reports a relationship with Siemens Healthineers, Bracco AG and Pfizer AG that includes: funding grants and speaking and lecture fees. Additionally, Wolfgang P. Fendler reports fees from SOFIE Bioscience (Research funding) and Bayer (consultant, speaker, research finding). If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. The other authors declare no conflict of interest regarding this manuscript., (Copyright © 2023 Elsevier Inc. All rights reserved.)