Pleomorphic Adenoma : Squamous Metaplasia

Clinical: Salivary gland neoplasms make up 2% to 6.5% of all neoplasms of head and neck region. They occur over a wide age range but the peak incidence is in 6th to 7th decades with a slight female predominance. Patients usually present with a well-defined painless swelling in front of or behind the ear (parotid tumors). The risk factors include radiation exposure, familial predisposition, tobacco use (smokers have 8 times higher risk of developing Warthin’s tumor than nonsmokers.), exposure to industrial chemicals, and certain viruses (EBV, HIV). Morphology: Majority of the salivary gland neoplasms involve the parotid gland. Approximately 75% of cases are benign and 80% to 90% are of epithelial origin. Benign neoplasms are more common in major salivary glands whereas malignant neoplasms represent greater proportion of the tumors in the minor salivary glands. The most common benign salivary gland neoplasm is pleomorphic adenoma. Most salivary gland tumors exhibit polymorphic growth pattern and some may have dual cell composition. The tumors are classified according to cell types of the normal salivary gland toward which they differentiate as epithelial, myoepithelial, ductal, and non-epithelial (mesenchymal). Morphologic features like invasion beyond capsule, perineural invasion, and lympho-vascular invasion are associated with malignancy. Due to overlapping histologic features between some benign and malignant salivary gland tumors, the distinction between them is not always possible in limited biopsies. In such cases, complete excision is recommended. Fine needle aspiration biopsy is a useful initial diagnostic tool in assessing a salivary gland neoplasm. Ref: 1. Atlas of Head and Neck Pathology by Bruce Wenig, MD, Third edition, 2016; 2. Pathologic basis of Disease, Eighth edition, 2010.