Abstract 2767: Simultaneous 18F-FDG PET/MR imaging for metastases identification in a disseminated human preclinical melanoma model

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Abstract Melanoma is a skin cancer at high risk of metastatic progression, hence associated with poorer prognosis. Imaging represents an essential tool to assess tumor stage, but also to monitor disease progression and therapy response. However, a single imaging technique cannot efficiently detect and characterize all metastases. Therefore, we evaluated the potential of simultaneous 18F-FDG PET/MR imaging in preclinical models of disseminated melanoma at different stages. Female Nude and SDRG rats were intravenously injected with CMEL 5 cells, originating from brain metastases of a human melanoma. On day (D) 60, 70, and 80 post-injection, Nude rats were imaged using brain T2-weighted (T2w) 7T MRI and whole-body simultaneous 18F-FDG (10-15 MBq) PET/MR. Furthermore, whole-body and brain T2w MR images were acquired using a 4.7T MRI on D20 and D34 post-injection in SDRG rats. Visual detection and quantitative analysis of lesions were performed on MRI or PET/MR images, and results were confronted with necropsy (melanin pigmented lesions) and gamma counting data. From D60 post-CMEL-5 cell injection, all Nude animals exhibited metastases in one to four different locations. Moreover, most of metastases locations found in clinical setting were detected in our experimental model using simultaneous 18F-FDG PET/MR imaging, even allowing the observation of brain lesions on T2w MR images. MRI further allowed precise contouring of each organ of interest to effectively identify bone, lung, adrenal and spleen metastases with enhanced 18F-FDG uptake. Additionally, PET image quantification in adrenals was consistent with gamma counting results. As anticipated, small lesions below PET spatial resolution limit (i.e. <1 mm) were not detected by imaging. SDRG rats displayed a faster and more homogenous tumor spread in brain, lungs and liver on MR images, while more metastases were seen during autopsy (additional spreading to pancreas, adrenals, reproductive system, bones, lymph nodes and skin). The experimental model of disseminated CMEL-5 melanoma in Nude rats demonstrates its ability to mimic the human pathology. Hence, it appears to be a promising tool to monitor therapy response and potentially recognize progression from pseudo-progression. Simultaneous PET/MR imaging has shown to be more effective than stand-alone techniques in detecting melanoma dissemination, except for brain and small lesions for which the PET data are altered by partial volume effect. Thus, by complementing previously acquired MR images from the novel SDRG rat model with simultaneously acquired PET images, we could also provide insights on this promising metastatic model. Citation Format: Alexandra Oudot, Peggy Provent, Alan Courteau, Nicolas Hoffmann, Melanie Guillemin, Jordan Longin, Sarah Belderbos, Bertrand Collin, Marc Hillairet de Boisferon, Alexandre Cochet, Cyril Berthet. Simultaneous 18F-FDG PET/MR imaging for metastases identification in a disseminated human preclinical melanoma model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2767.