Salivary gland tumor pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Simrat Sarai, M.D. [2]

Overview

The pathophysiology of salivary gland tumors depends on the histological subtype.^[1]

Pathophysiology

Pathogenesis

The parotid gland is the most frequent site of salivary gland tumors which accounts for approximately 80 to 85 percent of these tumors.^[2]^[3] About 75 percent of parotid lesions are benign and approximately 25 percent are malignant.^[4] Less frequently, salivary gland tumors originate in the sublingual, submandibular, and minor salivary glands, which are located throughout the submucosa of the upper aerodigestive tract and mouth.^[5]

In comparison to tumors arising in the parotid, 70 to 90 percent of sublingual gland tumors, 50 to 75 percent of minor salivary gland tumors, and 40 to 45 percent of submandibular gland tumors are malignant. Approximately 85% of salivary gland tumors occur in the parotid glands, followed by the minor salivary glands and submandibular, and approximately 1% occur in the sublingual glands. Overall approximately 80% of all parotid masses are benign.^[6]

Microscopic Pathology

Histologically, pleomorphic adenoma is the most common type of benign salivary gland tumor, which comprises about half of all salivary tumors. Other rarer benign salivary gland tumors include basal cell adenoma, Warthin tumor, and canalicular adenoma. The most common malignant salivary gland tumors are adenoid cystic carcinoma and mucoepidermoid carcinoma, which together constitute approximately one-half of all malignant salivary gland tumors.

Histological features of benign tumors

Tabular form - adapted from Libre Pathology


Entity	Architecture	Morphology	Cell borders	Cytoplasm	Nucleus	Differential Diagnosis	Other

Pleomorphic adenoma	Variable	Mixed proportion; must include: Myoepithelium Mesenchymal stroma Epithelium (ductal cells) or Chondromyxoid stroma	Variable	Variable	Plasmacytoid	Adenoid cystic carcinoma	Occasionally encapsulated, mixed proportion of glandular, myoepithelial and mesenchymal cells
Warthin tumor	Papillary, bilayer	Cuboid (basal), columnar (apical)	Clearly seen	Eosinophilic, abundant	Unremarkable	Sebaceous lymphadenoma	AKA papillary cystadenoma lymphomatosum
Basal cell adenoma	Variable, islands surrounded by hyaline bands, lesion encapsulated	Basaloid	Subtle	Scant, hyperchromatic	Granular	Basal cell adenocarcinoma
Canalicular adenoma	Chains of cells	Cuboid or columnar	Subtle	Scant, hyperchromatic	Granular	Basal cell adenoma	Exclusively oral cavity, 80% in upper lip; immunohistochemistry: p63-
Sialoblastoma	Variable, islands surrounded by loose fibrous stroma	Basaloid	Subtle	Scant, hyperchromatic	Granular	Adenoid cystic carcinoma	Basal cell adenocarcinoma

Histological features of malignant tumors


Entity	Architecture	Morphology	Cell borders	Cytoplasm	Nucleus	Differential Diagnosis	Other

Mucoepidermoid carcinoma	Cystic and solid	Epitheloid	Distinct	Fuffy, clear, abundant	Nuclei small	SCC (?)	Immunohistochemistry: p63+
Adenoid cystic carcinoma (AdCC)	Pseudocysts, cribriform, solid, hyaline stroma	Epitheloid	Subtle	Scant, hyperchromatic	Small+/-"carrot-shaped"	Pleomorphic adenoma, Polymorphous low grade adenocarcinoma (PLGA)	Stains: PAS+ (pseudocyst material), CD117+, cyclin D1+
Acinic cell carcinoma (AcCC)	Sheets, acinar (islands)	Epithelioid	Clear	Granular abundant	Stippled, +/-occasional nucleoli	Adenocarcinoma not otherwise specified, oncocytoma of salivary gland	Stains: PAS +ve, PAS-D +ve; Immunohistochemistry: S-100 -ve, p63 -ve
Salivary duct carcinoma	Glandular, cribriform	Columnar	Subtle/clear	Hyperchromatic	Columnar	Metastatic breast carcinoma	Similar to ductal breast carcinoma; male>female
Polymorphous low-grade adenocarcinoma	Variable, often small nests, may be targetoid	Epithelioid	Indistinct	Eosinophilic	Ovoid & small with small nucleoli	Adenoid cystic carcinoma (AdCC)	Minor salivary gland tumour, often in palate, cytologically monotonous; IHC: S-100+, CK+, vim.+, GFAP+/-, BCL2+/-
Epithelial-myoepithelial carcinoma	Nests (myoepithelial) with tubules (epithelial)	Epithelioid	Not distinct	Eosinophilic cytoplasm; epithelial: scant; myoepithelial: moderate	Focal clearing	Adenoid cystic carcinoma (AdCC), pleomorphic adenoma	Rare
Basal cell adenocarcinoma	Variable, islands surrounded by hyaline bands, lesion not encapsulated	Basaloid	Subtle	Scant, hyperchromatic	Granular	Basal cell adenoma	Rare, usually parotid gland, may arise from a basal cell adenoma