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

The value of [¹⁸F]FDG PET/CT imaging in the management of SMARCB1-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. Methods: 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 SUVmax 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. Results: 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 SUVmax, 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 SUVmax, 8.9; range, 1.8–27.0). Extranodal disease was observed in 36 patients, most commonly in the lungs (n = 24; median SUVmax, 5.8; range, 1.7–17.5) and bones (n = 19; median SUVmax,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 (n = 18), lymph nodes (n = 13), and soft tissues (n = 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. Conclusion: 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.