A clear cell variant of mucoepidermoid carcinoma harboring CRTC1-MAML2 fusion gene found in buccal mucosa: report of a case showing a large clear cell component and lacking typical epidermoid cells and intermediate cells

Abstract

The predominance of clear cells in mucoepidermoid carcinomas (MEC) is rare, and cases in which this occurs are termed clear cell variants of MEC. We present a case of a 70-year-old woman complaining of a right buccal mucosal mass, which had increased in size over 1 year. Histological examination revealed the mass to be composed predominantly of clear tumor cells, with mucin-containing cells and intermediate cell-like cells. Immunohistochemistry indicated that the tumor was positive for CK5/6 and p63, but negative for myoepithelial markers such as S-100 protein, αSMA, and calponin. These findings ruled out the possibility of a clear cell myoepithelial carcinoma, which is the most frequently observed type of salivary carcinoma composed predominantly of clear cells. However, it is difficult to distinguish between clear cell variants of MEC and hyalinizing clear cell carcinoma. Therefore, we performed fluorescence in situ hybridization to determine whether MAML2 rearrangement had occurred in this mass. Direct sequencing of the RT-PCR product demonstrated CRTC1-MAML2 fusion between exon 1 of CRTC1 and exon 2 of MAML2. Thus, the diagnosis of clear cell variant of MEC was confirmed. This is the first report of CRTC1-MAML2 fusion gene detection in a clear cell variant of MEC.

Central mucoepidermoid carcinoma arising from glandular odontogenic cyst confirmed by analysis of MAML2 rearrangement: A case report

“…It has been reported that the immunohistochemical profile of keratins may be helpful in differentiating diagnosis but not an absolute marker for distinction between GOC and MEC . On the other hand, MAML2 gene rearrangement is recently reported to specifically identify MEC both in salivary glands and jaws . In MEC, the rearrangement is identified in both the solid and GOC‐like cystic areas, while it is not in true GOC .…”

“…It is important to distinguish between central MEC and GOC, however, morphologic similarities may pose a difficulty in diagnosis . Recently, specific fusion genes for MEC, CRTC1‐MAML2 and CRTC3‐MAML2 , have been described . Their utility as a diagnostic adjunct in the distinction between central MEC and GOC has been highlighted because these genes are expressed in central MEC, but not in GOC .…”

“…[3][4][5] Recently, specific fusion genes for MEC, CRTC1-MAML2 and CRTC3-MAML2, have been described. [6][7][8][9][10][11][12][13][14][15] Their utility as a diagnostic adjunct in the distinction between central MEC and GOC has been highlighted because these genes are expressed in central MEC, but not in GOC. [5][6][7][8][9][10][11][12][13][14] Herein, we present a case of central MEC arising from GOC that was confirmed by the analysis of MAML2 rearrangement.…”

Primary Mucoepidermoid Carcinoma of the Lung with Prominent Clear Cells

“…Identifi cation of the CRTC1-MAML2 fusion gene is now considered to be pathognomonic for this entity, and the fusion gene can be detected by real-time PCR or FISH in both low-grade and high-grade MEC (3,5,7,8,13,14). Recent studies of PMEC demonstrate MAML2 rearrangement in 60% to 100% of tested cases (5,15,16) detected by FISH or real-time PCR.…”

“…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.…”