PMC8550837_01
Intraoral appearance of the buccal mucosa and CT image. (a) The mucosal epithelium was normal in color with a smooth surface. There was no induration around the tumor (black arrow). (b) CT (axial view) showed an enhanced lesion on the anterior portion of the right palatoglossal arch (yellow arrow).
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At the first visit, examination of the oral cavity demonstrated a mass measuring 15 x 10 mm in the right buccal mucosa on the anterior portion of the lobular polypoid palatoglossal arch (Figure 1(a)). CT showed an enhanced lesion on the anterior portion of the right palatoglossal arch (Figure 1(b)).
Microscopic and survey view of the surgical resected specimen. (a) Resected specimen measuring 18 x 12 x 14 mm. (b, c) The tumor demonstrated proliferation of tumor nests with a fibrous stroma. There was no capsule and no contact with the covering epithelium. (d) The tumor had invaded into surrounding muscle and adipose tissues. (e, f) The tumor nests were composed of epithelioid and clear cells partially surrounded by hyalinized stroma. Features suggestive of transition between the two cell types were observed (HE; original magnification: (b) x1, (c) x20, (d, f) x40, and (e) x100).
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The surgical specimen measured 18 x 12 x 14 mm (Figure 2(a)). There was no capsule and no contact with the covering epithelium (Figures 2(b) and 2(c)). The tumor invaded surrounding structures such as muscle and adipose tissue (Figure 2(d)). The tumor nests were composed of epithelioid and clear cells with partially hyalinized stroma (Figures 2(e) and 2(f)).
Special stains: (a) PAS, (b) d-PAS, (c) mucicarmine, and (d) Alcian blue. PAS stain shows positive cytoplasmic red material in the clear cells, but PAS with diastase stain was negative, suggesting the presence of glycogen. The contents of duct-like structures were positively stained by mucicarmine and Alcian blue, but mucus-producing cells were not evident in the tumor nests ((a-d) original magnification x200).
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Intracytoplasmic fine granules were positive for periodic acid-Schiff (PAS) and were negative for diastase-sensitive PAS (Figures 3(a) and 3(b)). The contents of duct-like structures were positively stained by mucicarmine and Alcian blue, but mucus-producing cells were not evident in the tumor nests (Figures 3(c) and 3(d)).
Immunohistochemical findings: (a) pancytokeratin (AE1/AE3), (b) p63, (c) S100, and (d) Ki-67. The tumor cells were stained intensely with cytokeratins, but not myoepithelial markers. The nuclei of the clear cells were positive for p63. Ki-67-positive cells were rarely found in the tumor nests ((a-d) original magnification x200).
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Immunohistochemically, the tumor cells were strongly positive for AE1/AE3 (Figure 4(a)), CK5/6, and p63 (Figure 4(b)), but negative for alpha-SMA and S100 (Figure 4(c)), and Ki-67-positive cells were rarely found in the tumor nests (Figure 4(d)).
FISH analysis: (a) EWSR1 break-apart; (b) CREM; (c) EWSR1-CREM gene fusion. EWSR1 break-apart FISH demonstrate a cell with split red and green signals, indicative of a translocation. This case demonstrated split positivity for EWSR1, and fusion with CREM was confirmed.
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Immunohistochemically, the tumor cells were strongly positive for AE1/AE3 (Figure 4(a)), CK5/6, and p63 (Figure 4(b)), but negative for alpha-SMA and S100 (Figure 4(c)), and Ki-67-positive cells were rarely found in the tumor nests (Figure 4(d)). Using bacterial artificial chromosome clone-derived DNA probes for EWSR1 and CREM (the names of BAC clones used will be provided upon request), fluorescence in situ hybridization (FISH) analysis revealed the presence of EWSR1-CREM (Figures 5(a)-5(c)).