Warthin-Like Mucoepidermoid Carcinoma: A Morphological Spectrum – A Report of 3 Cases with Histological and Cytological Findings and Review of the Literature

Abstract

<b><i>Background:</i></b> Mucoepidermoid carcinoma (MEC) showing Warthin’s tumor (WT)-like features is a low-grade malignancy which should be differentiated from WT. Morphological features may be distinctly different in each case, causing diagnostic difficulties. <b><i>Case Presentation:</i></b> Three cases were presented and discussed with their morphologies. All cases that presented with a mass in the parotid gland went to parotidectomy, and all had preoperative fine-needle aspirations (FNAs). Case 1 was a 16-year-old female; FNA was suggestive of WT and initially interpreted as WT histologically. Case 2 was a 27-year-old male; FNA was interpreted as noninformative due to the presence of cyst fluid only. Case 3 was a 53-year-old male and cytologically was found to be suspicious for MEC which contained squamous and goblet cells on a mucoid background. On histopathological examination, case 2 and case 3 were morphologically consistent with low-grade MEC with WT-like features. Prominent lymphoid stroma and the cystic pattern were the characters of these tumors. Case 1 had the classical WT appearance with some mucinous and squamous metaplasia which could only be interpreted as MEC after the detection of MAML2 rearrangement by FISH. The other 2 showed either focal or relatively diffuse usual low-grade MEC findings, and case 3 was also confirmed by MAML2 rearrangement. <b><i>Conclusion:</i></b> Cytological and histopathological features revealed a spectrum. Differentiating WT-like MECs from ordinary WTs may be challenging. On the one end of the spectrum, they may look very much like WT, and on the other end, even though usual MEC features are present, still, WT-like appearance may pose diagnostic difficulty. Showing MAML2 rearrangement in these cases is very helpful. The presence of mucinous and squamous cells in an otherwise WT-like looking tumor should be alarming for MEC, and if possible, each case should be analyzed for MAML2 rearrangement.

Mucoepidermoid carcinoma: Analysis of 76 cytologic cases and correlation with histologic grade

“…Because WT is typically cystic and may undergo both squamous and mucinous metaplasia, it is among the most commonly confused SG neoplasms with MEC 7,23,35–46 . Klijanienko et al however profess to never having encountered an example in their large series of MEC, or an example of MEC in their large series of WT 11,47 .…”

“…Our single benign neoplasm diagnosis was called WT (case 42, Figure 8) presumably due to the presence of oncocytic cells and innumerable lymphocytes even though background mucin was documented. Oncocytic‐type cells were seen in 22% of conventional MEC cases from the series of Wade et al 8 From 3 cases of Warthin‐like MEC, Basak et al 36 described 1 appearing as classic WT but containing mucinous and squamous metaplasia. A correct interpretation of MEC was made only after positive MAML2 rearrangement.…”

“…Because WT is typically cystic and may undergo both squamous and mucinous metaplasia, it is among the most commonly confused SG neoplasms with MEC. 7,23,[35][36][37][38][39][40][41][42][43][44][45][46] never having encountered an example in their large series of MEC, or an example of MEC in their large series of WT. 11,47 Mucinous WT is not uncommon, however, Zhang et al 48 encountered mucinous metaplasia in 24 WTs (83%), with 14% having an abundant amount.…”

Cystic Salivary Gland Neoplasms: Diagnostic Approach With a Focus on Ancillary Studies

“…12 MAML2 testing has become particularly useful as multiple morphologic variants of MEC are now known. [14][15][16] MAML2 fusion testing can therefore be applied in a diagnostic workup whenever MEC is in the differential. Ciliated and Warthinlike variants of MEC have recently been described, and may be impossible to diagnose without molecular testing for MAML2 gene fusion.…”

“…16 The presence of squamous and mucinous cells in a Warthin tumor should be cautiously interpreted. 16 While mucinous metaplasia in Warthin tumor is a well-recognized phenomenon, it can be a frequent diagnostic pitfall. 17 A MAML2 FISH analysis revealed that all Warthin tumors with mucinous metaplasia lacked MAML2 fusion and only 1 case of Warthin-like MEC harbored MAML2 rearrangement.…”