Polymorphous low-grade adenocarcinoma of the salivary gland, PLGA

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.

Histopathology

The tumour is well circumscribed at low power, but the margins show foci of infiltration. There are various architectural patters:

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

cytokeratin	positive
AE1/AE3	21/212
CK7	21/212
CK20	0/212
EMA	positive
S-100	positive
bcl-2	positive
vimentin	positive
CD117	may be positive1
actin	variably focal/weak
CEA	focal or negative1
GFAP	usually negative, at most only focal1
Calponin	negative1

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.

1 Perez-Ordonez B. Selected topics in salivary gland tumour pathology. Current Diagnostic Pathology2003;9:355-365.

2 Meer S,Altini M. CK7+/CK20- immunoexpression profile is typical of salivary gland neoplasia. Histopathology 2007; 51:26-32

This page last revised 4.8.2007.