PMC6458882_01
Histopathological findings of the parotid gland mass. (a) A low-power view shows two morphologically distinct lesions immediately adjacent to each other: mucoepidermoid carcinoma (upper left) and basal cell adenoma (lower right) with a sharp transition between the two components. (b) The basal cell adenoma component demonstrates jigsaw-like nests of basaloid cells surrounded by a ribbon-like rim of eosinophilic hyaline material. (c) The mucoepidermoid carcinoma component shows numerous plump mucocytes with finely granular clear cytoplasm as well as polygonal epidermoid cells and intermediate cells. (d) A mucicarmine special stain confirms the presence of intracytoplasmic and extracellular mucin associated with the lesional cells of the mucoepidermoid carcinoma.
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fig1
Histologic examination of the nodule showed two distinct lesional components that were well-demarcated from each other with no transition zone (Figure 1(a)). Distinct, dense ribbons of eosinophilic hyaline material were noted surrounding the islands of tumor cells (Figure 1(b)). The lesional cells consisted of an admixture of mucous cells (mucocytes), polygonal epidermoid cells, and intermediate cells (Figure 1(c)). A special stain for mucicarmine highlighted intracellular mucin within the mucocytes as well as the extracellular mucin (Figure 1(d)).
Immunohistochemical findings of the parotid gland mass. (a) A CK5/6 stain highlights the peripheral abluminal squamoid cells in mucoepidermoid carcinoma (upper left) as well as a prominent abluminal myoepithelial cell population in the basal cell adenoma (lower middle). (b) Similarly, p63 shows peripheral positivity in both tumor components. (c) A stain for CK7 highlights mucocytes and cells adjacent to glandular lumens in the mucoepidermoid carcinoma and patchy cells throughout the basal cell adenoma with a subset of luminal cells staining intensely. (d) The proliferation index as estimated by an immunohistochemical stain for Ki-67 is approximately 3-4% in the mucoepidermoid carcinoma; the basal cell adenoma is no longer present in the deeper level used for immunohistochemistry.
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fig2
Immunohistochemical stains for p63 and CK5/6 highlighted a prominent abluminal population, and CK7 highlighted patchy cells throughout, with a subset of luminal cells staining intensely (Figure 2). The Ki-67 proliferation index was approximately 3-4% (Figure 2).