Histopathology

PLGA is characterized by cytologic uniformity, histologic diversity, and an infil trative growth pattern. The tumour cells are small to medium size and uniform in shape with bland, minimally hyperchro-matic, oval nuclei and only occasional nucleoli. Mitoses are uncommon and necrosis is not typical. The striking feature of these carcinomas is the variety of morphologic configurations between tumours and within an individual tumour. The main microscopic patterns are: 1) lobular, 2) papillary or papillary-cystic (typically focal), 3) cribriform areas sometimes resembling those in adenoid cystic carcinoma, and 4) trabecular or small, duct-like structures lined by a single layer of cuboidal cells. The cells form concentric whorls or targetoid arrangements around blood vessels or nerves. Foci of oncocytic, clear, squamous or mucous cells may be found. Stroma may show areas of mucinosis or hyalinization. Despite the innocuous cytologic appearance, the neoplasm always invades adjacent soft tissues and is uncapsulated. Neurotropism is common in PLGA. Invasion of adjacent bone may be seen in tumours of the palate or mandible.

Immunohistochemistry

The neoplastic cells of PLGA are immunoreactive with antibodies to cytok-eratin (100%), vimentin (100%), S-100 protein (97%), carcinoembryonic antigen (54%), glial fibrillary acidic protein (GFAP) (15%), muscle specific actin (13%), and epithelial membrane antigen (12%) {342,2011,2763}. Expression of galectin 3 has been reported to be significant in PLGA {2006}. Bcl-2 is over expressed in most cases of PLGA {342,2011}.

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