PMC4575733_01
(a) Gross appearance of the surgical specimen showing a well-demarcated and vaguely lobulated ivory-white tumor. (b) Pancreatic parenchyma was haphazardly distributed in the tumor. (c) Spindle cells proliferated in heavily collagenized fibrous stroma. (d) Concentric elastic fibers in the duct walls were not evident with Elastica van Gieson staining.
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fig1
The specimen resected from the pancreas contained a white, well-demarcated solid nodule, measuring 21 x 17 mm, with a homogeneous appearance on its cut surface (Figure 1(a)). The cellularity of the spindle cells was low in most areas, but there were a few hypercellular areas where the spindle cells haphazardly proliferated (Figures 1(b) and 1(c)). Concentric elastic fibers in the duct walls were not evident with Elastica van Gieson staining (Figure 1(d)).
Spindle cells were immune-positive for (a) CD34, (b) CD99, and (c) bcl-2. (d) Ductal epithelia were immune-positive for S-100.
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fig2
Immunohistochemically, the spindle cells were positive for CD34, CD99, and bcl-2 (Figures 2(a)-2(c)) but negative for alpha-SMA, c-kit, DOG1, desmin, S-100, and calretinin. The ductal epithelia were positive for cytokeratin 7 and S-100 protein (Figure 2(d)).
(a) Immunohistochemically, STAT6 was highly expressed in the nuclei of the spindle cells. The results of (b) RT-PCR and (c) sequencing analysis indicated that NAB2 exon 4 fused to STAT6 exon 2.
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Immunohistochemical study revealed that STAT6 was highly expressed in the nuclei of the spindle cells (Figure 3(a)). The primer set of NAB2 exon 3 and STAT6 exon 3 was only able to amplify the product (Figure 3(b)). The direct sequence of the product (PRISM 3730 DNA Analyzer, Hokkaido System Science Co., Ltd., Sapporo, Japan) revealed the gene fusion between NAB2 exon 4 and STAT6 exon 2 (Figure 3(c)).