[1300] Spectrum of Problematic Metaplastic Changes in Salivary Gland Tumors

Douglas R Gnepp, Evgeny Yakirevich, Samir K El-Mofty. Rhode Island Hospital, Providence, RI; Washington University, St. Louis, MO

Background: Metaplastic change is a common phenomenon in salivary gland neoplasms. Most of these tumors easily fit into specific diagnostic categories. However, rare tumors present diagnostic challenges due to prominent metaplastic changes. In this study we analyzed the spectrum of salivary gland metaplastic changes causing diagnostic difficulty over a 20-year period.
Design: 56 salivary gland neoplasms with prominent metaplastic change were retrieved from pathology and consultation files (1990-2010). Ancillary studies (histochemistry, immunohistochemistry & EM) were applied as necessary.
Results: Patients' age ranged from 17-87 (median 55) years with an equal male: female ratio. 45 cases originated from the parotid, 2 from submandibular and 9 from the minor salivary glands. Metaplastic changes were analyzed separately for epithelial, myoepithelial and stromal components. Epithelial metaplastic changes included, in descending order, squamous, oncocytic, mucoepidermoid, adenoid-cystic, and mucinous metaplasia. Myoepithelial cells demonstrated oncocytic, epithelial-myoepithelial, and adenoid-cystic like changes; the stromal component showed occasional lipomatous metaplasia. 36% showed more than one type of differentiation. Prominent squamous metaplasia was the most common metaplastic phenomenon and was most frequently associated with pleomorphic adenomas (PA) (14 of 26 cases) and Warthins tumor (9 cases); it was also seen in 2 oncocytomas. Diffuse oncocytic metaplasia was a characteristic feature of 20 tumors, including 8 PA, 5 acinic cell carcinomas, 2 mucoepidermoid carcinomas, 2 myoepitheliomas, 2 cystadenomas & 1 epithelial-myoepithelial carcinoma. Less frequent metaplastic changes included prominent mucoepidermoid (3), adenoid-cystic (3), mucinous (2), & epithelial-myoepithelial (1) differentiation. All the less frequent changes were seen exclusively in PA. Careful sampling and light microscopy looking for absence of destructive overgrowth of benign elements, lack of perineural, vascular, or extracapsular invasion & bland nuclear features will support a diagnosis of a benign metaplastic salivary gland tumor. Recognizing foci of residual classical appearing tumor in addition to the more prominent metaplastic component will allow proper classification.
Conclusions: Prominent metaplastic changes, although rare, may occasionally obscure the true nature of a salivary gland neoplasm. Recognizing the spectrum of metaplastic change will aid in establishing proper diagnoses and treatment.
Category: Head & Neck

Tuesday, March 20, 2012 1:00 PM

Poster Session IV # 167, Tuesday Afternoon


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