Pleomorphic adenoma pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Cafer Zorkun M.D., PhD.

Overview

Pleomorphic adenoma is a benign neoplastic tumour of the salivary glands. It is the most common type of salivary gland tumour and the most common tumour of the parotid gland. It derives its name from the architectural pleomorphism (variable appearance) seen by light microscopy. It is also known as "Mixed tumor, salivary gland type", which describes its pleomorphic appearance as opposed to its dual origin from epithelial and myoepithelial elements.

Pathophysiology

Histologically, it is highly variable in appearance, even within individual tumours. It is characterized by an admixture of epithelial and myoepithelial elements in a variable background stroma that may be mucoid, myxoid, cartilaginous or hyaline. Epithelial elements may be arranged in duct-like structures, sheets, clumps and/or interlacing strands and consist of polygonal, spindle or stellate-shaped cells (hence pleomorphism). Areas of squamous metaplasia and epithelial pearls may be present. The tumour is usually enveloped by a fibrous capsule of varying thickness and often incomplete. The tumour often extends through these discontinuities but is not a sign of malignant transformation as it does not invade surrounding tissues.