case_images: PMC11361973_01
case_images: Imaging and immunohistochemical staining related to the pathological diagnosis of malignant solitary fibrous tumor. (A, B), MRI shows that the tumor is located subcutaneously in the occipital region, with clear boundaries. On T1WI, it shows iso-low signal intensity, while on T2Flair, it shows mixed high signal intensity. (C), Microscopic observation shows that the boundary of the tumor was clear and appeared to have a fibrous pseudo capsule; 100x magnification. (D), The tumor cells are epithelioid with eosinophilic cytoplasm, and the stroma in some areas was hyaline; 400x magnification. (E), Collagen deposition can be seen between tumor cells, resembling sclerosis, and some areas of collagen fibers show nodular growth; 200x magnification. (F), necrosis can be seen in the tumor, and dense tumor cells can grow around blood vessels around the necrotic area; 100x magnification. (G), Immunohistochemical analysis showed diffuse strong expression of STAT6 protein in tumor cells; 100x magnification. (H), EWSR1 FISH detection showed that the proportion of cells with red-green separation signals was about 22%.
case_images: fonc-14-1339582-g001.jpg
case_images: PMC11361973_01_fonc-14-1339582-g001.jpg
case_images: f1
case_images: T1WI ( Figure 1A ) and mixed high signal in T2Flair ( Figure 1B ). There was no previous history of cancer. The histopathological investigation of the removed mass revealed the following. (1) Gross examination: one nodule, 4.0 cmx3.8 cmx3.3 cm, encased in a capsule, with a gray-white solid texture on the cut surface. (2) Microscopic examination: the boundary of the tumor was clear and appeared to have a fibrous pseudo capsule ( Figure 1C ); the tumor cells were epithelioid, the cytoplasm was eosinophilic, and the stroma in some areas was hyaline ( Figure 1D ); the nuclei of the tumor cells were moderately heterogeneous, the nuclei were vacuolated, small nucleoli were visible, and the nuclear pleomorphism and mitosis were about 6/10 high power field (HFP). Collagen deposition was visible between tumor cells, as well as sclerosis, with collagen fibers forming in a knot-like pattern in one region ( Figure 1E ). Tumor cells in other regions became degenerated and necrotic, and tumor cells in the vicinity of the necrotic areas were shown to develop densely around the blood vessels ( Figure 1F ). Immunohistochemical analysis showed diffuse strong expression of STAT6 protein in tumor cells ( Figure 1G ), CD99, Vimentin, INI1, Calponin, BCOR, and focally positively expressed CK, CD34, SMA, and sporadically expressed TLE1, and did not express CK20, P63, FLI-1, NKX2.2, S100, Myoegnin, WT-1, CyclinD1, SATB2, CD3, CD20, CD43, and Ki-67 value-added index of about 10%. Furthermore, the molecular pathology examination suggested that the EWSR1 FISH assay count was positive (the percentage of cells with red and green separated signals was about 22%,  Figure 1H ).
case_images: NGS detected dual fusion of the NAB2-STAT6 gene, including STAT6 exon 15-NAB2 exon 7 (A) and NAB2 exon 7-STAT6 exon 16 (B).
case_images: fonc-14-1339582-g002.jpg
case_images: PMC11361973_01_fonc-14-1339582-g002.jpg
case_images: f2
case_images: RNA-seq detected the fusion of the NAB2 and STAT6 genes and the presence of two fusion isoforms at the same time, namely, STAT6ex15-NAB2ex7 ( Figure 2A ) and NAB2ex7-STAT6 exon 16 ( Figure 2B ). (NAB2: NM_005967.3, STAT6: NM_003153.4).