39919317

Comparison of 68Ga-FAPI and 18F-FDG PET/CT Findings in Oncocytic and Conventional Subtypes of Pediatric Adrenocortical Carcinoma

Elnaz Jenabi, MD,* Hamidreza Amini, MD,¡ Bababk Nikkholgh, MD,* and Ghasemali Divband, MD+

Abstract: Adrenocortical carcinoma, a poor prognosis cancer with a low survival rate, is a rare pediatric malignancy. We performed 18F-FDG PET/CT and 68Ga-FAPI PET/CT imaging in 2 children with different subtypes of adrenocortical carcinoma and compared the findings. FAPI PET/CT revealed superior performance in patient with conventional subtype and in detecting skeletal lesions. However, the recurrent lesions in the surgical bed had higher FDG uptake in both patients.

Key Words: 68Ga-FAPI PET/CT, 18F-FDG PET/CT, adrenocort- ical carcinoma, pediatric cancer imaging (Clin Nucl Med 2025;50:e665-e667)

Received for publication December 8, 2024; accepted December 11, 2024.

From the *Central Gamma Scan, Tehran, Iran; and }Khatam PET/CT Center, Tehran, Iran.

Conflicts of interest and sources of funding: none declared.

Correspondence to: Ghasemali Divband, MD, Khatam PET/CT Cen- ter, Tehran, Iran. E-mail: divband_ali@yahoo.com.

Copyright @ 2025 Wolters Kluwer Health, Inc. All rights reserved. DOI: 10.1097/RLU.0000000000005705

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FIGURE 1. A 15-year-old girl with the oncocytic subtype of adrenocortical carcinoma (ACC) underwent left adrenalectomy and left adnexal metastasis resection, followed by chemotherapy. For disease restaging, the patient was referred for 18F-FDG PET/CT imaging. Also, 68Ga-FAPI PET/CT scan was performed as a part of a clinical trial. The MIP (A and E), transaxial fused 18F-FDG PET/CT, transaxial CT, and transaxial 68Ga-FAPI PET/CT images (B-D) revealed pulmonary metastasis (FDG vs FAPI SUVmax: 2.5 vs 1.2, B), as well as tumoral lesions within surgical bed and left upper abdomen (SUVmax: 14 vs 4.4, C), and left infrarenal space (SUVmax: 12 vs 3.8, D). The diffuse FDG and FAPI uptake in the fibroglandular tissue of both breasts was related to increased estrogen levels associated with the menstrual cycle.

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FIGURE 2. A 9-year-old boy underwent left adrenalectomy and right frontal metastasectomy for conventional ACC, followed by chemoradiation therapy. The patient was referred for 18F-FDG PET/CT imaging to evaluate response to treatment. In addition, as a part of a clinical trial, 68Ga-FAPI PET/CT was also performed. The MIP (A and E), transaxial fused 18F-FDG PET/CT, transaxial CT, and transaxial 68Ga-FAPI PET/CT images (B-D) revealed considerable FAPI uptake in non-FDG-avid metastatic lesions within the left frontal lobe (SUVmax: 3.3, B) and liver segment VI lesion (SUVmax: 3.2, C). However, the recurrent lesion within the surgical bed showed higher FDG uptake (SUVmax: 9.1 vs 3.6, D).

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FIGURE 3. The transaxial fused 18F-FDG PET/CT, transaxial CT, and transaxial 68Ga-FAPI PET/CT images of the patient with oncocytic ACC (A and B) and the other patient with conventional ACC (C and D) revealed intense FAPI uptake in the faintly FDG avid skeletal metastases (white arrows). Childhood ACC is a rare malignancy accounting for less than 0.2% of all pediatric cancers. The oncocytic subtype of ACC is a very rare variant, with about 200 cases reported in the literature so far.1-3 68Ga-FAPI, a novel promising PET/CT imaging agent, is currently applied in multiple clinical trials for detection of different malignancies and associated metastases.4,5 In this case series, FAPI PET/CT appeared as an excellent diagnostic imaging tool in detecting metastatic conventional ACC and skeletal lesions of both subtypes. However, the recurrent lesions in the surgical bed revealed higher FDG uptake in both patients, a finding that was previously described in a case of adult recurrent ACC.6 Some previous studies have shown the superiority of 68Ga-FAPI PET/CT imaging in diagnosis of different types of primary and metastatic lesions compared with the 18F-FDG PET/CT, especially in detecting liver, bone, and brain metastases.7-9 However, some other studies demonstrated better performance of FDG PET/CT in different malignancies.10-12 The findings of these 2 cases indicate that integrating 68Ga-FAPI PET/CT imaging with 18F-FDG PET/CT studies in patients with ACC enhances the diagnostic sensitivity. In addition, the possibility of radionuclide therapy can be evaluated with 68Ga-FAPI-based imaging.

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