All are true about pleomorphic adenoma EXCEPT:
Correct Answer: Malignant transformation risk is high
Description: ANSWER: (A) Malignant transformation risk is highREF: Robbin s 8th ed chapter 16, Sabiston 18th ed chapter 33See PLATE P-18 A KEY PLATE P-18 KEYSALIVARY GLAND TUMORS(A) PLEOMORPHIC ADENOMAMorphology. Most pleomorphic adenomas present as rounded, well-demarcated masses rarely exceeding 6 cm in the greatest dimension. Although they are encapsulated, in some locations (particularly the palate) the capsule is not fully developed, and expansile growth produces protrusions into the surrounding gland, rendering enucleation of the tumor hazardous. The cut surface is gray-white with myxoid and blue translucent areas of chondroid.The dominant histologic feature is the great heterogeneity mentioned. In the typical morphology' epithelial.'' myoepithelial areas (right arrowhead) are punctuated by myxochondroid areas (arrows). The epithelial elements resembling ductal cells or myoepithelial cells are arranged in duct formations, acini, irregular tubules, strands, or sheets of cells. These elements are typically' dispersed within a mesenchyme-like background of loose myxoid tissue containing islands of chondroid and, rarely, foci of bone. Sometimes the epithelial cells form well-developed ducts lined by cuboidal to columnar cells with an underlying layer of deeply' chromatic, small myoepithelial cells. In other instances there may be strands or sheets of myoepithelial cells. Islands of well-differentiated squamous epithelium may also be present. In most cases there is no epithelial dysplasia or evident mitotic activity.(B) WARTHIN'S TUMOR:Most Warthin tumors are round to oval, encapsulated masses, 2 to 5 cm in diameter, usually arising in the superficial parotid gland, where they are readily palpable. Transection reveals a pale gray' surface punctuated by narrow' cystic or deftlike spaces filled with a mudnous or serous secretion.On microscopic examination there is Papillary projections lined by a double layer of neoplastic epithelial cells resting on a dense lymphoid stroma sometimes bearing germinal centers. Outer oncocytic layer of columnar cells having an abundant, finely granular, eosinophilic cytoplasm (red arrow'). Secretory cells are dispersed in the columnar cell layer, accounting for the secretions within the cystically dilated lumens. Inner oncocytic lay'er of cuboidal to polygonal cells (green arrow) resting on lymphoid stroma (yreilow arrow)(C) MUCOEPIDERMOID CARCINOMA: Mucoepidermoid carcinomas can grow as large as 8 cm in diameter and although they are apparently circumscribed, they lack well-defined capsules and are often infiltrative at the margins. Pale and gray-white on transection, they frequently contain small, mucin-containing cysts. The basic histologic pattern is that of cords, sheets, or cystic configurations three distinct cell lines of squamous/ epidermoid cells (long white arrow), mucous cells (black arrow), or intermediate cells (short white arrow). The hybrid cell types often have squamous features, with small to large mucus-filled vacuoles, best seen when highlighted with mucin stains. The tumor cells may be regular and benign appearing or, alternatively, highly anaplastic and unmistakably malignant. Accordingly, mucoepidermoid carcinomas are subclassified into low, intermediate, or high grade.(D) ADENOID CYSTIC CARCINOMA: In gross appearance, they are generally small, poorly encapsulated, infiltrative, gray-pink lesions. On histologic evaluation, they are composed of multiple basaloid epithelial cells having dark, compact nuclei and scant cytoplasm arranged in cribriform architecture (arrow A) with perineural invasion (arrow B). The spaces between the tumor cells are often filled with a hyaline material thought to represent excess basement membrane. Pleomorphic adenoma is a benign, encapsulated mixed tumor of parotid gland. Malignant mixed tumors include both cancers originating from pleomorphic adenomas, termed carcinoma ex pleomorphic adenoma, and de novo malignant mixed tumors. The risk for malignant transformation of benign pleomorphic adenomas is 1.5% within the first 5 years but increases to 9.5% once the benign tumor has been present for more than 15 years.
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Surgery
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