PMC8429901_01
Histological findings of GNET. Low power view shows a sheet like pattern with ulceration on the surface [(A), X100]. Patchy lymphocytic infiltration and multiple lymphoid follicles were observed in the tumor border near the serosa [(B), X100]. The neoplastic cells arranged in microcystic [(C), X200], papillary [(D), X100], fascicular [(E), X100], palisade [(F), X100], pseudoalveolar [(G), X200] or rosette like [(H), X200] pattern with eosinophilic cytoplasm. Some areas showed epithelioid cells with clear cytoplasm [(I), X400].
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The tumor was centered in the muscularis propria with focal extension to the mucosa and ulcer formation (Figure 1A). Peritumoral lymphocytic infiltration and lymphoid follicles were observed (Figures 1B-I).
Immunohistochemical and molecular findings of GNET. The neoplastic cells expressed S-100 [(A), X200] and intact SMARCA4(BRG1) [(B), X100]. Syn [(C), X200] was focally positive. The Ki67 [(D), X200] proliferative index was low. Staining for pancytokeratin [(E), X200] was negative. FISH using EWSR1 break apart probe showed red and green split apart signals, suggesting EWSR1 gene rearrangement [(F), X1000].
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The Ki-67 index was low (about 5%) (Figures 2A-E). Fluorescence in situ hybridization (FISH) using EWSR1 break apart probe (Abbott Molecular, Des Plaines, IL) at 22q12 (Figure 2F) showed split EWSR1 signals in the tumor cells, indicating the presence of EWSR1 rearrangement.
Histologic features of the SMARCA4-deficient undifferentiated carcinoma. The neoplastic cells involved the mucosa [(A), X100]. Higher magnification showed several glands [(B), X400], noncohesive rhabdoid cells [(C), X400], multiple necrosis [(D), X200], patchy lymphocytes and plasma cells infiltration [(E), X400], obvious mitotic figures [(F), X400], multinucleated tumor cells [(G), X400] and large cells [(H), X400]. Multiple lymphovascular permeation was present [(I), X400].
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Scattered multinucleated tumor cells and irregular large cells were focally noted (Figures 3A-H). There was extensive lymphovascular invasion (Figure 3I).
Immunohistochemical and molecular findings of the SMARCA4-deficient undifferentiated carcinoma. The tumor cells diffusely expressed pancytokeratin [(A), X200] and vimentin [(B), X200] with paranuclear accentuation. The Ki67 [(C), X200] proliferative index was high. The tumor showed intact expression of INI1 [(D), X200] and complete loss of SMARCA4(BRG1) [(E), X200, upper right]. No EWSR1 gene rearrangement was revealed by FISH [(F), X1000].
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INI1 protein expression was intact, whereas complete loss of SMARCA4(BRG1) was observed (Figures 4A-E). The absence of EWSR1 rearrangement was also confirmed by FISH using EWSR1 break apart probe (Abbott Molecular, Des Plaines, IL) at 22q12 (Figure 4F).
NGS-based comprehensive genomic profiling revealed EWSR1-CREB1 fusion (A) in the GNET component and SMARCA4 frame-shift mutation [c.4882_4886dup(p.Lys1630fs)] (B) and KRAS hotspot missense mutation [c.183A>T(p.Gln61His)] (C) in the SMARCA4-deficient undifferentiated carcinoma component, respectively.
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Further next-generation sequencing (NGS) analysis of this tumor in the ileum revealed EWSR1-CREB1 fusion (Figure 5A). Lys1630fs)] (Figure 5B), which might lead to protein truncation and loss of expression, rather than EWSR1-CREB1 fusion.