Mucoepidermoid carcinoma of the palate composed exclusively of clear cells (clear cell variant)

Abstract

To the Editor, Mucoepidermoid carcinoma (MC) of the salivary glands is a malignant epithelial tumor that is composed of varying proportions of mucus, epidermoid, intermediate, columnar, and clear cells [2]. It is classified into low-, intermediate-, and high-grade types on the basis of morphologic and cytologic features [2, 6]. Although mucous, intermediate, and epidermoid cells are predominant in most MCs, it is well known that clear cells very infrequently predominate over other cell types [1, 2, 3, 4, 5]. Such cases are called clear cell variant of MC [1, 2, 3, 4, 5]. The authors here report a rare case of MC of the palate composed exclusively of clear cells.A 42-year-old Japanese man presented a palate mass measuring approximately 2 cm in diameter. The mass in the palate was whitish pink and relatively hard in consistency. The overlying mucosa showed mild hyperemia. A needle biopsy was performed, and it showed clear cells that were arranged in a medullary, solid pattern (Fig. 1). The clear cells had small hyperchromatic nuclei and abundant clear cytoplasm. A low-grade malignant tumor was suspected pathologically, and the tumor was excised with wide margins. Scrutiny of visceral organs including kidneys showed no remarkable changes. The patient is now free of disease 11 months after the operation.Grossly, the resected tumor measured 202012 mm and was whitish tan in color and relatively hard in consistency. The mucosal surface showed mild erosion. Histologically, the tumor was composed exclusively of clear tumor cells (Fig. 2A). They were arranged in a medullary, sheet-like, and solid pattern separated by thin fibrous septae (Fig. 2B). Invasions into the surrounding mucosa and minor salivary glands were recognized. Clusters of non-clear cells having small hyperchromatic nuclei and small acidophilic cytoplasm were noted in a very few areas (Fig. 2C). They were regarded as intermediate cells. These cells appeared to merge with the clear cells (Fig. 2C). Relatively large cells with mucus in the cytoplasm were scattered in a very small number (Fig. 2D). These cells were considered as mucous cells. The proportions of clear cells, intermediate cells, and mucous cells were approximately 95%, 4%, and less than 1%, respectively. The surgical margins were negative for tumor cells. Cytologically, the clear cells showed small hyperchromatic nuclei that were centrally located in the cytoplasm (Fig. 2B). The cytoplasm was clear, and cell membranes were clearly recognized. Neither keratinization nor intercellular bridges were recognized. The intermediate cells showed small hyperchromatic nuclei and small acidophilic cytoplasm (Fig. 2C). The mucous cells show acidophilic mucin-like materials in the cytoplasm T. Terada ( ) ) · S. Ikeuchi

Comparative Cytokeratin Expression in the Different Cell Types of Salivary Gland Mucoepidermoid Carcinoma

“…In our study, squamous cells were observed in almost all cases, followed by intermediate and mucous cells, confirming the predominance of these three cellular types in MEC. Clear cells, although less commonly found, are usually arranged in lobular or solid nests that can eventually be the predominant architectural finding, giving rise to the so-called clear cell variant of MEC [1,25]. Columnar cells were observed in about one-third of the cases, usually lining cystic and ductal structures, and we could also identify two cases with nests of oncocytic cells, an uncommon finding in MEC [1,26].…”

“…In fact, MEC is characterized by a variety of cell types and growth patterns, which also include intermediate, clear, columnar, and oncocytic cells, arranged in solid nests and cystic or ductal structures [1,5,6,11,25,26]. This cellular heterogeneity contributes to the difficulties in understanding its histogenesis.…”

EWSR1‐ATF1 fusion is a novel and consistent finding in hyalinizing clear‐cell carcinoma of salivary gland

“…The largest two of these reports show all 15 cases arising in oral cavity (Pires et al, 2010;Yang and Chen, 2010). The remaining reports of pure ''clear-cell MEC'' have been case studies from oral cavity, nasal cavity, conjunctiva, and larynx (Seo et al, 1980;Peison et al, 1988;Terada et al, 2004;Kapur et al, 2005;de Prado et al, 2007). This is unusual in light of the typical distribution of conventional MEC in major salivary gland in half of all cases (Goode et al, 2005).…”

Primary Mucoepidermoid Carcinoma of the Lung with Prominent Clear Cells

“…It typically arises in the minor salivary glandtype epithelium of the large central airways (2)(3)(4)(5). Occasionally, mucoepidermoid carcinoma (MEC) demonstrates prominent cytoplasmic clearing (6)(7)(8)(9)(10), and on biopsy, the presence of these clear cells can pose a diagnostic challenge for pathologists. We present a case of PMEC with prominent clear cells.…”