Polymorphous low-grade adenocarcinoma is a low-grade, infiltrative tumour
characterized by diverse architectural patterns, but bland looking tumour
(2) In 1984, polymorphous low-grade adenocarcinoma was first defined by Evans and Batsakis as a malignant tumour arising in the minor salivary glands previously reported as lobular carcinoma or terminal duct carcinoma.
(3) This tumour is regarded as the second most common malignant tumour in the minor salivary glands.
A few cases have been reported in the major salivary glands, usually as malignant component in carcinoma ex pleomorphic adenoma.
Hard palate is the most frequently involved site of the head and neck. Cases have been reported in other sites like buccal mucosa, upper lip, base of the tongue and retromolar area.
(4) Polymorphous low-grade adenocarcinoma occurs more frequently in women affecting patients mainly in the sixth and seventh decade of life.
(5) Clinically, the tumour presents as an indolent asymptomatic swelling but occasionally can be painful and even ulcerate.
(6) Macroscopically, most tumours are circumscribed but non-encapsulated, with a light tan to gray glistening cut surface.
(7) The tumour is characterized by single-layer strands of cells that can form lobular, tubular, cribriform, trabecular, papillary-cystic and cystic histological patterns.
The stroma appears either strongly eosinophilic and hyalinized, or muco-hyalinized with a bluish tint.
Clear cells in nests are also observed in the lobular subtype.
Foci of residual salivary gland acini surrounded by neoplastic cells are occasionally found.
Peri-neural invasion by groups of tumor cells is a frequent finding.
Psammoma-like structures are occasionally observed.
This tumour frequently presents with prominent vascularity.
(8) The tumour cells show diffuse moderate to strong immunoreactivity for cytokeratin7, EMA and S100 protein.
(9)Pleomorphic adenoma and adenoid cystic carcinoma are the most important differential diagnosis of polymorphous low-grade adenocarcinoma.
In contrast to polymorphous low-grade adenocarcinoma, pleomorphic adenoma is a non-infiltrative tumour with dual luminal and abluminal cell differentiation. Positive staining for GFAP in a mesenchymal-like cell population adjacent to epithelial nests is commonly noted in pleomorphic adenoma but not in polymorphous low-grade adenocarcinoma.
Because polymorphous low-grade adenocarcinoma and adenoid cystic carcinoma have different prognoses with respect to risk of local recurrence, distant metastasis, and death due to the neoplasm, it is important to distinguish these two neoplasms. Both can show similar architectural patterns, e.g. cribriform architecture.
Most adenoid cystic carcinomas show admixture of the cribriform pattern with tubular or solid patterns. ACC characteristically contains abundant myoepithelial (abluminal) cells with increased nuclear-to-cytoplasmic ratio and basaloid (hyperchromatic) angulated nuclei without identifiable nucleoli. In contrast, basaloid hyperchromatic nuclei are not generally evident in PLGA, which typically consists of cells with vesicular chromatin and inconspicuous small nucleoli. Smooth muscle actin immunoreactivity is expected in the majority of adenoid cystic carcinoma, but in a minority of polymorphous low-grade adenocarcinoma.
(10) Polymorphous low-grade adenocarcinoma is very rarely associated with regional and distant metastasis.
(11) The nature of the disease is generally indolent, and the prognosis is relatively good. Wide surgical resection is recommended as a primary treatment, and the role of radiotherapy is controversial.
De Araujo VC, Passador-Santos F, Turssi C, Soares AB, de Araujo NS. Polymorphous low-grade adenocarcinoma: an analysis of epidemiological studies and hints for pathologists. Diagnostic Pathology. 2013;8:6.
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