FDG PET/MRI and PET/CT Findings in a Case of Lung Metastases From Infantile Fibrosarcoma Harboring LMNA-NTRK1 Gene Fusion.

Infantile fibrosarcoma is a rare fibroblastic tumor of intermediate malignancy predominantly seen in infants. We describe FDG PET/MRI and PET/CT findings in a pediatric patient with multiple lung metastases from infantile fibrosarcoma harboring LMNA-NTRK1 gene fusion 8 years after resection of the primary tumor in the left hand. The lung metastases appeared as multiple nodules with irregular or smooth margins in both lungs and showed variable FDG uptake, ranging from low-grade to high-grade activity, which may reflect different biologic behavior of these tumors. The lung tumors disappeared or decreased significantly in size after tropomyosin receptor kinase inhibitor therapy.