Predominantly oncocytic mucoepidermoid carcinoma of palate: A case report

Abstract

Oncocytic mucoepidermoid carcinoma (OMEC) is an uncommon variant of mucoepidermoid carcinoma. Histopathologically, it is characterised by the predominance of cells with large polygonal morphology and with an abundance of eosinophilic granules. We present a rare case of OMEC manifested as painless palatal swelling in a 25-year-old young male. The overlying mucosa was normal in appearance, with no evidence of ulceration or discharge. Histopathology examination showed the presence of sheets of mucous and intermediate cells along with cystic areas of variable sizes and shapes. On high power magnification, oncocytes were evident, showing abundant granular eosinophilic cytoplasm with central dark round nuclei. Around 75-80% tumour cell population was composed of oncocytic cells. The predominant presence of oncocytes can present diagnostic difficulties to pathologists due to overlapping features with adenoid cystic carcinoma, oncocytoma, acinic cell carcinoma, Warthin's tumour, and other oncocyte tumours. Although the presence of oncocytes is a pathognomonic feature, the role of immunohistochemistry and genetic analysis in diagnosis is discussed in the present paper. Moreover, considering its behaviour as a low-grade MEC, it is prudent to avoid an aggressive treatment strategy and prevent unwarranted morbidity. We recommend prospective studies to better understand the factors that influence the prognosis of OMEC.

Keywords: MAML2 rearrangement; oncocytic mucoepidermoid carcinoma; palatal swelling.

Figure 1

(a) Intraoral preoperative clinical picture showing swelling involving the right side of the hard palate with normal overlying mucosa. (b) Unencapsulated tumour showing sheets of mucous and intermediate cells along with cystic areas of variable sizes and shapes (hematoxylin-eosin, Total magnification x100). (c and d) The cystic spaces were lined by oncocytic cells showing abundant granular eosinophilic cytoplasm with central dark round nuclei (black arrow). Inset in c and d shows a higher magnified view of the cells from the select areas. (hematoxylin-eosin; total magnification x400)