This is a low-grade malignancy characterised by bland cytology and various architectural patterns.
Epidemiology
This tumour constitutes 19.6% of malignant salivary gland tumours1.
Clinical features
Patients are usually middle-aged to elderly, more often women. Minor salivary glands of the palate, buccal mucosa, upper lip. retromolar region, floor of mouth, posterior tongue or nasal cavity may be involved. Involvement of major salivary glands is uncommon, but PLGA may occur as the carcinomatous component of carcinoma ex-pleomorphic adenoma.
tubules and ducts, lined by a single layer of cells.
solid nests
cystic, cribriform and papillary: these are only seen in one third of tumours and never predominate.
cords and trabeculae, predominantly at the margins of the tumour
The tumour cells are embedded within a myxoid or mucohyaline stroma. Perineural infiltrations is the rule and perivascular infiltration common: cells often surround these structures in a targetoid arrangement. Psammoma bodies may be present.
The cells are bland and are variable small cuboidal, round, polygonal or spindle. Chromatin is fine and nucleoli are not prominent. The mitotic rate is about 1/10HPF. Atypical mitoses are not seen.
Immunohistochemistry
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positive |
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positive |
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positive |
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positive |
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positive |
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may be positive1 |
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actin |
variably focal/weak |
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focal or negative1 |
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usually negative, at most only focal1 |
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negative1 |
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Differential diagnosis
Pleomorphic tumour; tubules are lined by two layers of cells. There may be squamous differentiation and cartilage, not seen in PLGA. There is no perineural invasion. These tumours are positive for GFAP and calponin.
Adenoid cystic carcinoma; cells are more basaloid with a higher N/C ratio and more hyperchromatic nuclei. Tubules and ducts are composed of two cell layers.
adenocarcinoma NOS
Prognosis
There may be progression to high grade carcinoma after several recurrences.
References
Diagnostic histopathology of tumors. Edited by CDM Fletcher. 2nd edition. Churchill Livingstone. Page 275.
1Perez-Ordonez B. Selected topics in salivary gland tumour pathology. Current Diagnostic Pathology2003;9:355-365.
This page last revised 31.1.2004.