A 56-year-old woman presented with a cystic mass involving the ventral surface of her tongue. An excision was performed and yielded the tissue shown in the images below.
There is a large central cyst lined by a variable epithelial component that ranges from attenuated squamous mucosa to more proliferative elements, as seen in the low-power image above. The epithelial elements are heterogeneous and include squamoid, oncocytic and mucin-producing cells, as well as intermediate cells. An infiltrative component is seen surrounding the central cyst.
What is your diagnosis?
After the last very difficult case, it's time for a rather straightforward one. This is a nice example of a mucoepidermoid carcinoma, presumably arising from the minor salivary glands of the tongue. The cellular heterogeneity is the best clue to the diagnosis, as no other salivary gland tumor, except perhaps mixed tumor, contains such an admixture of squamous, mucinous, oncocytic, intermediate and occasionally clear cell elements.
The cystic component of the present lesion is lined by cells with very uniform nuclei, albeit considerable variation in cytoplasmic differentiation. However the infiltrative component surrounding the cyst is composed predominantly of squamoid cells with somewhat larger and slightly more pleomorphic nuclei. Because of this invasive component, I would diagnose this case as an intermediate grade mucoepidermoid carcinoma. Had the lesion been entirely intracystic the chance of recurrent or metastatic disease would have been essentially zero. The infiltrative nature of the current case suggests a small but real concern for local recurrence or regional metastasis.
As is often the case, the current example contains a clear-cut component of oncocytes. This was discussed in an early case with a predominant oncocytic component. Immunoreactivity for p63 is of value in the distinction from oncocytomas, as this is not present in the latter tumors, but is a common feature of all mucoepidermoid carcinomas.
Recent studies have demonstrated that low- and intermediate-grade mucoepidermoid carcinomas, including the oncocytic vaiants, harbor a characteristic t(11;19) translocation that results in a MECT1-MAML2 fusion gene. This translocation is present in approximately 70% of low-and intermediate-grade tumors, but is notably absent from high-grade mucoepidermoid carcinomas. A commercially available breakapart FISH probe is available and can be used for for this distinction as well.