EWSR1-NFATC2 and FUS-NFATC2 Gene Fusion-Associated Mesenchymal Tumors: Clinicopathologic Correlation and Literature Review

Figure 4

Symptomatic bone lesion in the metaphysis of the right proximal humerus of a 12-year-old boy. (a) CT and (b) MRI imaging demonstrated an irregular, partially osteolytic lesion. (c) Core biopsy revealed giant cells (arrows) containing bland spindle cell proliferation. (d) Curettage showed similar lesional tissue without necrosis, pleomorphism, or mitotic activity; however, a conspicuous biphasic pattern was observed (d, f). The distinctive spindle cell population contained siderin and mast cells and expressed immunohistochemically EMA (g) and CD99 (not shown), while the adjacent EMA and CD99 negative areas showed SMA expression (h). (e) FISH analysis with a break-apart probe demonstrated one fused (arrowhead) and one split (arrows) signal, indicating the rearrangement of the FUS gene.