Pleomorphic adenoma (PA), the most common salivary gland tumor, accounts for 54 to
65% of all salivary gland neoplasias and 80% of the benign salivary gland tumors. It
most frequently affects the parotid gland, followed by the submandibular and the
minor salivary glands. Microscopically, mucous, sebaceous, oncocytic and squamous
metaplasia, sometimes with the formation of keratin pearls, may be present, but the
latter rarely results in the formation of extensive keratin-filled cysts lined by
squamous epithelium. Extensive squamous metaplasia can be mistaken for malignancy,
including mucoepidermoid carcinoma and squamous cell carcinoma. Here, we present an
unusual case of PA with extensive squamous metaplasia and keratin cyst formations in
a minor salivary gland, and discuss its microscopic features, including the
immunohistochemical characteristics, and differential diagnosis of this uncommon
presentation.
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