Clinicopathological practice in the differential diagnosis of mucoepidermoid carcinoma from neoplasms with mucinous component

Abstract

Background: The differential diagnosis of mucoepidermoid carcinoma (MEC) from neoplasm undergoing mucinous features brings more pitfalls to pathologists. Combining specific MAML2 gene rearrangement and histological characteristics may be the solution. Methods: Twenty-five tumors with mucinous components were selected for differential diagnosis of MEC. All the cases were detected for MAML2 gene rearrangement. The cases diagnosed as MEC were classified into four variants: classic, oncocytic, Warthin-like, and nonclassified, and they were graded using the Brandwein system. The histological characteristics of non-MECs were summarized for differential diagnosis. Univariate survival analysis was performed on MECs. Results: There were 16 MECs; 62.5% were MAML2 rearranged. For the low-, intermediate-, and high-grade MECs, the rate of rearrangement was 83.3%, 100%, and 28.6%, respectively. Both the oncocytic and Warthinlike MECs were MAML2 rearranged. For the classic and nonclassified MECs without MAML2 rearrangement, non-keratinized squamoid cells and distinctive mucinous cells were essential diagnostic criteria. On survival analysis, all the disease progression occurred in high-grade MECs (p = 0.038). Nine cases were diagnosed as non-MECs: pleomorphic adenoma with mucinous metaplasia showed no ex-capsular involvement; metaplastic Warthin tumor appeared with overt keratinization and residual oncocytic bilayered epithelium; mix squamous cell and glandular papilloma showed an endobronchial papillary growing pattern; adenosquamous carcinoma was accompanied by squamous carcinoma in situ of the overlying mucosa. All the non-MECs were negative for MAML2 rearrangement. Conclusion:The application of combining MAML2 rearrangement and histological characteristics is helpful in the differential diagnosis between MEC and other tumors with mucinous components.

Pleomorphic Adenoma with Extensive Mucinous Metaplasia Mimicking Mucoepidermoid Carcinoma: A Case Report and Literature Review

“…These tumors are often high-grade and invasive. 4 In the literature we have accessed in the last 20 years, we have compiled Table 1 summarizing case reports that raise suspicion of malignant salivary gland tumors due to widespread metaplastic changes in the PA. 1,[6][7][8][9][10][11][12][13][14] In this case, a prior FNAB performed elsewhere prompted the excision of the lesion. While evaluating fine needle aspiration biopsies of pleomorphic adenomas can be challenging due to their diverse metaplastic components, the Milan reporting system may place such aspirates in risk categories (III, IVA, IVB, V, or even VI).…”

Salivary Gland Neoplasms With a Unique Trabecular Histology and MAML2 Translocation

“…14 For example, MEC devoid of mucocytes can be challenging to differentiate from mammary analog secretory carcinoma with squamoid cell mimickers, 18 and oncocytic MEC with limited amount of both mucus-secreting cells and squamoid cells can be difficult when distinguishing from oncocytic carcinoma, acinar cell carcinoma, and adenocarcinoma, not otherwise specified. 19 Therefore, acknowledging the diverse morphologic patterns of MEC is important for pathologists to make a proper diagnosis which requires further molecular testing. In particular, similar to the p63 negativity of our cases, Bishop et al 15 recently reported 10 MAML2 fusion-confirmed MEC cases that are devoid of squamous cells both histologically and immunohistochemically and also emphasized the need for updated definition of the MEC.…”

“…Notably, however, even with the routinely available ancillary tests, pathologists frequently encounter troublesome cases in which immunostaining is not useful 14 . For example, MEC devoid of mucocytes can be challenging to differentiate from mammary analog secretory carcinoma with squamoid cell mimickers, 18 and oncocytic MEC with limited amount of both mucus-secreting cells and squamoid cells can be difficult when distinguishing from oncocytic carcinoma, acinar cell carcinoma, and adenocarcinoma, not otherwise specified 19 . Therefore, acknowledging the diverse morphologic patterns of MEC is important for pathologists to make a proper diagnosis which requires further molecular testing.…”