PMC8727594_01
Case report timeline.
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A chronological summary of the case report is shown in  Figure 1 .
Radiological imaging and macroscopic findings of primary site. (A) Enhanced abdominal CT showing central necrosis and the marked enhancement of anterior to left periphery of the tumor. At the right periphery, the tumor is seen invading the pelvic wall (white arrow). (B) 18F-fluorodeoxyglucose-positron emission tomography showing the marked hypermetabolism in the right invasive area of the tumor. (C) Autopsy specimen, with a well-circumscribed and smooth area (left side: gray arrow) and poorly margined and lobulated area (right side: white arrow).
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Marked hypermetabolism in the invasive area of the tumor was seen on 18F-fluorodeoxyglucose-positron emission tomography (FDG PET) ( Figures 2A, B ) and both CT and FDG PET revealed multiple lung and bone metastases.   Figure 2C  shows the gross findings from the tumor autopsy, namely a well-circumscribed and smooth area on the left side and a poorly margined and lobulated area on the right side corresponding to radiological imaging findings ( Figures 2A, B ).
Primary Site Pathology. Pathologic findings were distinct between the left (A-E) and right (F-J) sides of the tumor. On the left side (gray arrow in 
Figure 2C
), spindle-shaped tumor cells with mild atypia and collagen fiber proliferation are seen (A). Ki-67 positive cells were around 1% (B). Tumor cells positively stained with CD34 (C), STAT6 (D) and CD99 (E). On the right side (white arrow in 
Figure 2C
), round or short spindle-shaped tumor cells with high N/C ratios proliferating in a honeycomb pattern are seen (F). Around 80% of tumor cells were positive for Ki-67 (G) and CD99 (J) but not CD34 (H) or STAT6 (I). Scale bar: 50microm.
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Pathological findings also differed between the left ( Figures 3A-E ) and right sides ( Figures 3F-J ) of the tumor. The Ki-67-positive rate was low, around 1% ( Figure 3B ), but cells were diffusely stained with CD34 ( Figure 3C ) and tumor cell nuclei were positively stained with STAT6 ( Figure 3D ). Moreover, the around 80% of these tumor cells were stained with Ki-67 ( Figure 3G ) but completely negative for CD34 and STAT6 ( Figures 3H, I ). Figures 3E, J ), focally positive for BCL-2, and negative for p53 (data not shown). From these observations, the left side lesion was considered to be the differentiated SFT while the right side lesion was composed of a dedifferentiated tumor.
NAB2-STAT6 fusion gene status in primary and metastatic sites. (A) Agarose gel separation of a NAB2-STAT6 fusion-specific RT-PCR product (NAB2ex6/STAT6ex16, Lane 4) from the primary differentiated tumor. (B) Detection of NAB2ex6/STAT6ex16 fusion gene from the primary site (differentiated and dedifferentiated tumors) and metastatic sites. (C) Sanger sequencing chromatogram of a NAB2/STAT6 fusion-specific RT-PCR product. Dif: differentiated tumor. Dedif: dedifferentiated tumor.
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The NAB2 exon 6/STAT6 exon 16 (NAB2ex6/STAT6ex16) variant was identified in the primary differentiated tumor ( Figure 4A ), with Sanger sequencing revealing a stretch (111bp) of NAB2 intronic sequence between the NAB2 exon 6 and STAT6 exon 16 ( Figure 4B ). The NAB2ex6/STAT6ex16 variant was also detected in the primary dedifferentiated tumor and lung/liver metastases ( Figure 4C ), albeit at lower levels compared to the primary differentiated tumor.
Characteristics of genomic alterations in primary and metastatic sites. (A) Number of all gene mutations between primary differentiated and dedifferentiated tumors. (B) Number of all gene mutations between primary and metastatic sites in dedifferentiated tumors. (C) Mutational heatmap for the primary differentiated tumor, primary dedifferentiated tumor, and lung/liver metastases. Mutations with variant allele frequency <10% were excluded.
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Tables 2-5 . The number of gene mutations was 164 in the primary differentiated tumor, 105 in the primary dedifferentiated tumor, 69 in the lung metastasis and 139 in the liver metastasis ( Figures 5A, B ). Mutations with variant allele frequency <10% were excluded from further analysis to clarify the significance of the mutations and a summary is shown in  Figure 5C .