Reclassification of a spindle cell sarcoma after identification of a TFG-ROS1 fusion: A case demonstrating the clinical benefit of next-generation sequencing in sarcoma

Background: Inflammatory myofibroblastic tumors (IMTs) are rare mesenchymal soft tissue sarcomas that often present diagnostic challenges due to their wide and varied morphology. A subset of IMTs have fusions involving ALK or ROS1. The role of next-generation sequencing (NGS) for classification of unselected sarcomas remains controversial. Methods and Results: We report a case of a metastatic sarcoma in a 34-year-old female originally diagnosed as an unclassified spindle cell sarcoma with myofibroblastic differentiation and later reclassified as IMT after NGS revealed a TFG-ROS1 rearrangement. Histologically, the neoplasm had spindle cell morphology with a lobulated to focally infiltrative growth pattern with scant inflammatory cell infiltrate. Immunohistochemistry demonstrated focal desmin and variable smooth muscle actin staining but was negative for SOX10, S100, and CD34. Fluorescence in situ hybridization was negative for USP6 or ALK gene rearrangements. NGS revealed a TFG-ROS1 rearrangement and the patient was treated with crizotinib with clinical benefit. Conclusions: We discuss the role of NGS as well as its potential benefit in patients with unresectable, ALK-negative metastatic disease. Considering this case and previous literature, we support the use of NGS for patients requiring systemic treatment.