Abstract:

Previously well-described in salivary glands, myoepithelial neoplasms are only more recently recognized to occur in soft tissue. This may be because these tumors have a broad range of cytologic and architectural features. On histologic examination, these tumors can have a variety of cellular structures that are found within a hyaline or chondroid stroma. The cells can grow in various patterns, including reticular, nested, trabecular, and solid, and have cytoplasm that is typically eosinophilic, clear, or vacuolated. This wide array of morphological findings leads to a spectrum of diagnoses for myoepithelial neoplasms, ranging from mixed tumors to myoepitheliomas to myoepithelial carcinoma. Immunohistochemical studies are also crucial to identification of these tumors. A panel should include keratin, EMA, S100, and GFAP. Mixed tumors, previously known as chondroid syringomas, differ from both myoepitheliomas and myoepithelial carcinoma in that they display ductal differentiation within a chondroid matrix. We present two cases of mixed tumors with prominent myoepithelial differentiation that presented as slow-growing, non-tender soft tissue masses that were subsequently re-excised due to their atypical appearance. Although most myoepithelial neoplasms follow an indolent, benign course, moderate cellular atypia and possibly myoepithelial differentiation raises concern for malignancy and a more aggressive course. Because of their prominent myoepithelial differentiation, these mixed tumors highlight the spectrum of myoepithelial neoplasms and allow us to point out key differences in the histopathological diagnosis of each subtype of myoepithelial tumor.

Financial Disclosure:
No current or relevant financial relationships exist.

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Allie Preston, MD