Pleomorphic Adenoma (PA, mixed tumor)

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A firm, long-standing nodule on the upper lip should also make a clinician think of the most common benign neoplasm of the salivary gland origin, which is pleomorphic adenoma (PA). The age and gender of this patient are not typical of PA, but this condition should nonetheless be included on the differential diagnosis of a swelling of the upper lip. The histology in this case, however, was not supportive of PA.

Pleomorphic adenoma is the most common benign salivary gland neoplasm of both the major and minor salivary glands. It originates from the myoepithelial cells and the reserve cells of the intercalated ducts. It accounts for 80% of all benign salivary gland neoplasms. It occurs in both major and minor salivary glands and accounts for up to 77% of parotid, 68% of submandibular, and 43% of minor salivary gland tumors. It is most common in females 30-50 years of age, but it is also described in children. One study reports 1% of cases affecting children under 10 years of age and 5.9% of cases occurring in patients between the ages of 10 and 20. PA presents as a small, painless, slowly enlarging nodule. If left untreated, it can enlarge significantly, sometimes increasing by several pounds in weight. It occurs in the oral cavity, especially the palate and lips. On the palate, it is usually located in the posterior hard palate or anterior soft palate but can also be in the posterior soft palate; PA usually occurs in the posterior and lateral palate, as opposed to torus palatines, which usually occurs in the middle hard palate and in the anterior. The posterior hard palate mixed tumor is fixed due to the bone-bound anatomy of the region; the tumor is otherwise movable. Histologically, mixed tumor has a wide variety of cellular and pattern manifestations. The main cellular components are epithelial duct-like structures and mesenchymal-like tissue such as myxochondroid matrix. These lesions are generally encapsulated, ranging from predominantly myxoid (36%) to extremely cellular (12%). Complete surgical removal with clean margins is the preferred treatment. Palatal lesions respond well to excision in one piece with the periosteum and overlying mucosa. Pleomorphic adenoma has a good prognosis, but it has a tendency for recurrence (up to 44%) if not treated thoroughly. The risk of recurrence is less if it occurs in the minor salivary glands (up to 20%). The risk of malignant transformation is about 5%.