Renal Medullary Carcinoma: Utility of [¹⁸F]FDG PET/CT in Evaluating Extent of Disease and Impact on Treatment Management.

Abstract

The value of [¹⁸F]FDG PET/CT imaging in the management of <i>SMARCB1</i>-deficient renal medullary carcinoma (RMC), a rare and aggressive type of kidney cancer, has not been established. We sought to determine the utility of [¹⁸F]FDG PET/CT findings for the evaluation of disease burden and treatment planning in patients with RMC. <b>Methods:</b> Using an institutional database, we identified patients with RMC who underwent [¹⁸F]FDG PET/CT scans as part of clinical care between 2016 and 2025. When available, baseline [¹⁸F]FDG PET/CT images were used; otherwise, the earliest available follow-up scan performed because of concern of recurrence or progression was included. For all scans, sites of abnormal [¹⁸F]FDG uptake were assessed, the SUV_max of the most avid site was quantified, and tumor-to-normal tissue ratios (TNRs) were calculated. PET/CT findings were compared with anatomic imaging (CT/MRI-based) performed within 30 d. Instances in which PET/CT findings altered treatment were recorded. <b>Results:</b> On PET, 48 of 49 patients had clearly [¹⁸F]FDG-avid disease. The single patient without [¹⁸F]FDG-avid lesions also lacked evidence of disease on anatomic imaging. Of the 23 patients who received a baseline PET/CT scan for staging purposes, 15 had intact renal primary tumors, and all tumors were [¹⁸F]FDG-avid (median SUV_max, 13.4; range, 9.5-23.5; median TNR blood, 10.7; range, 4.2-16.6). Ten patients were imaged during therapy, and 16 underwent imaging after progression or before the start of a new treatment. Forty-three patients had [¹⁸F]FDG-avid nodal metastatic disease (median SUV_max, 8.9; range, 1.8-27.0). Extranodal disease was observed in 36 patients, most commonly in the lungs (<i>n</i> = 24; median SUV_max, 5.8; range, 1.7-17.5) and bones (<i>n</i> = 19; median SUV_max,10.7; range, 3.7-24.8). In 31 patients, [¹⁸F]FDG PET/CT identified additional lesions not detected on anatomic imaging, predominantly involving bones (<i>n</i> = 18), lymph nodes (<i>n</i> = 13), and soft tissues (<i>n</i> = 11). These additional findings led to a change in clinical management for 10 (21%) of 48 patients with active disease. In contrast, no lesions were identified on anatomic imaging that were not apparent on PET/CT scans. <b>Conclusion:</b> RMC is a highly [¹⁸F]FDG-avid malignancy. [¹⁸F]FDG PET frequently detects additional metastatic sites missed by conventional anatomic imaging, facilitating disease extent assessment and optimizing treatment strategy in patients with RMC.