Tuesday 13 July 2010
Definition: Pleomorphic adenoma, also called benign mixed tumor, is the most common tumor of the salivary glands. About 90% of these tumors occur in the parotid gland and 10% in the minor salivary glands.
The most common sites of pleomorphic adenoma of the minor salivary glands are the palates followed by lips and cheeks. Other rare sites include the throat, floor of the mouth, tongue, tonsil, pharynx, retromolar area and nasal cavity.
Pleomorphic adenomas are benign salivary gland tumors that represent about 3- 10% of the neoplasm of the head and neck region. They are the most common tumors (50%) of the major and minor salivary glands.
The palate is considered as the most common intraoral site (42.8-68.8%), followed by the upper lip (10.1%) and cheek (5.5%).
Other rare sites include the throat (2.5%), retromolar region (0.7%), floor of the mouth and the alveolar mucosa.
Pleomorphic adenoma occurs more frequently in women than in men and is most common from the fourth to sixth decades with a mean age of 43-46 years.
Salivary gland tumors are rare in children and when they do arise, they preferentially affect major salivary glands, but minor salivary gland tumors have also been reported.
Pleomorphic adenoma usually presents as a mobile slowly growing, painless firm swelling that does not cause ulceration of the overlying mucosa.
Pleomorphic adenoma consists of cells with epithelial and mesenchymal differentiation (mixed tumor).
The highly variable morphology of this neoplasm is the result of interplay between these elements. Now it is widely accepted that both epithelial and mesenchymal (myxoid, hyaline, chondroid, osseous) elements often arise from same cell clone, which may be a myoepithelial or ductal reserve cell. There is no difference in behavior of this neoplasm based on proportion of various elements.
A monoclonal pattern is seen in the stromal, epithelial elements in the majority of cases. These findings suggest that the stromal and epithelial cells in pleomorphic adenomas of salivary gland arise from the same clone in most cases.
Variants of pleomorphic adenoma include:
pleomorphic adenoma with lipomatous change
myxoliopmatous pleomorphic adenoma
pleomorphic adenoma with squamous differentiation
benign metastasizing mixed tumor.
salivary pleomorphic adenoma
mammary pleomorphic adenoma
pleomorphic adenoma of the cheek (diagnosticpathology.org case report)
Cutaneous adnexal differentiation and stromal metaplasia in palate pleomorphic adenomas: a potential diagnostic pitfall that may be mistaken for malignancy. Schmidt LA, Olsen SH, McHugh JB. Am J Surg Pathol. 2010 Aug;34(8):1205-10. PMID: 20661019