case_images: PMC10765539_01
case_images: Imaging findings. The contrast-enhanced computed tomography showed a hypodense mass occupying the left side of the posterior mediastinal paravertebral region (arrow).
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case_images: The histological and immunohistochemical results of the tumor. (A) The lesion was composed of fibrous stroma and myxoid areas with an abrupt transition [hematoxylin and eosin staining (H&E); magnification: x40]. (B) The classic myxoid areas and fibrous stroma were shown in the tumor (H&E; magnification: x100). (C) Neoplastic cells were spindle-shaped and arranged in a whorled and short fascicular pattern (H&E; magnification: x200). (D) Some areas had increased cellularity with moderate atypia (H&E; magnification: x400) with the identification of mitotic figure (arrow) [(E) H&E; magnification: x400]. (F) The tumor cells showing diffuse and strong positivity for MUC4 (magnification: x400).
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case_images: Microscopically, the lesion was relatively well delineated and composed of fibrous stroma and myxoid areas with an abrupt transition ( Figures 2A, B ). The tumor cells were spindle and oval-shaped, arranged in a whorled and short fascicular pattern ( Figure 2C ). In some areas, the lesion had increased cellularity, and the neoplastic cells had spindled hyperchromatic nuclei showing moderate atypia, with indistinct pale eosinophilic cytoplasm and a few visible nucleoli ( Figure 2D ), and mitotic figures were identified without atypical forms (2/10 high power fields) ( Figure 2E ). Immunohistochemically, all the tumor components stained diffusely and strongly positive for MUC4 ( Figure 2F ).
case_images: Molecular findings. (A) Fluorescence in-situ hybridization demonstrated the presence of FUS gene rearrangement in the neoplastic cells [separation of the red (white arrowhead) and green (white arrow) signals]. (B) Next-generation sequencing-based technology revealed the breakpoint of FUS (exon 7) and CREB3L2 (exon 5) fusion transcript. (C) Sanger sequencing analysis confirmed the presence of the FUS::CREB3L2 fusion gene.
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case_images: The FISH results demonstrated the presence of FUS gene rearrangement ( Figure 3A ). A fusion transcript of FUS (exon 7, transcript NM_004960.3) and CREB3L2 (exon 5, NM_194071.4) was discovered ( Figure 3B ). Then, we further validated the presence of the FUS::CREB3L2 fusion transcript by PCR (polymerase chain reaction) and Sanger sequencing using primers (FUS-forward: 5'-GTCTGATTGTTCATTTGCAGA-3' and CREB3L2-reverse: 5'-GACTCAGAGGGCAGCCTGAGT-3') ( Figure 3C ).