26 July 2006 – Case of the Week #54
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We thank Dr. Sarah Webb, Harris Methodist HEB, Bedford, Texas (USA) for contributing this case. We invite you to contribute a Case of the Week by sending an email to NPernick@PathologyOutlines.com with microscopic images (any size, we will shrink if necessary) in JPG or GIF format, a short clinical history, your diagnosis and any other images (gross, immunostains, EM, etc.) that may be helpful or interesting. We will write the discussion (unless you want to), list you as the contributor, and send you a check for $35 (US) for your time after we send out the case. Please only send cases with a definitive diagnosis.
Case of the Week #54
Clinical history
The patient is a 59 year old woman with a slow growing tumor of the parotid gland present for several years. Upon excision, it was 3 cm, mottled and tan-yellow with scalloped borders.
Microscopic images: low power, high power #1, #2, AE1-AE3, S100
There was also peripheral soft tissue invasion and necrosis.
What is your diagnosis?
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Diagnosis:
Epithelial-myoepithelial carcinoma of the salivary gland
Discussion
Epithelial-myoepithelial carcinoma is a rare salivary gland tumor, representing less than 0.5% of tumors at this site. Most (80%) cases arise in the parotid gland and occur in women (60%), with a mean patient age of 60 years or older.
Grossly, these tumors are well circumscribed, up to 3 cm, and infiltrate into adjacent tissue. Microscopically, they are a low grade malignancy with epithelial and myoepithelial components. They are often multinodular with a thick fibrous capsule. Most tumor cells have myoepithelial features, with clear cytoplasm or naked nuclei. Focally, there are ducts or tubules with an outer rim of myoepithelial cells and inner, dark ductal cells. The ductal cells have scant eosinophilic cytoplasm and round, bland nuclei. These tumors may also have spindled or plasmacytoid cells.
The myoepithelial component is PAS+, diastase sensitive due to cytoplasmic glycogen. The myoepithelial component is also immunoreactive for S100, p63 (Cancer 2005;105:240), and smooth muscle actin, with variable keratin staining. The epithelial component is strongly immunoreactive for keratin and EMA, with occasional S100 staining.
Cytologic smears are usually cellular, with single cells and naked nuclei. A biphasic pattern may not be evident since the clear cells have fragile cytoplasm and often appear as naked nuclei (Diagn Cytopathol 2003;28:163)
These tumors are low grade malignancies with frequent local recurrences. They were previously often considered to be benign. However, with sufficient follow-up, there are rare regional nodal metastases and distant metastases to the lung and kidney.
The differential diagnosis may be broad. It includes myoepithelial carcinoma, which many authors define as lacking any epithelial component (Am J Surg Pathol 2000;24:761). Pleomorphic adenomas are also biphasic tumors, but have a prominent myxochondroid stroma, and the myoepithelial cells usually lack cytoplasmic clearing. Other biphasic tumors include adenoid cystic carcinoma (prominent cribriform pattern) and polymorphous low grade adenocarcinoma (affects intraoral salivary glands, clear cells do not predominate and are not associated with ductal cells). Clear cell carcinomas usually affect the minor salivary glands, are unencapsulated, lack epithelial cells and are negative for myoepithelial markers. Finally, metastatic renal cell carcinoma should be considered.
Additional references: Arch Pathol Lab Med 2002;126:676
Nat Pernick, M.D.
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