Pleomorphic adenoma of the salivary gland

A pleomorphic adenoma is the most common neoplasm of the salivary glands, accounting for 50% of all salivary gland tumours, and for 70% of all parotid tumours.

90% occur in the parotid. The remainder are found in the submandibular, sublingual, or accessory salivary glands. Most present in middle age or later but any age may be affected. It is the most common cause of a lump in the parotid or submandibular gland.

Pleomorphic adenoma affects both sexes approximately equally

• a Jordanian study revealed a slight male preponderance (males 56%) in incidence (1).

This tumour is regarded as benign but lacks true encapsulation, may infiltrate surrounding tissue, and may recur. The less differentiated tumours may be difficult to distinguish from frank carcinoma, and may metastasize to cervical lymph nodes or less commonly, through the blood stream to the lungs (2).

Notes:

• although clinically and histologically a pleomorphic adenoma benign tumour, there are rare reports of metastasis to regional and distant sites, in which the metastatic foci are histologically identical to the benign primary tumour (2)
  • often there is a long interval between the diagnosis of the primary tumour and the metastasis
  • propensity for malignant transformation (either clinical or histological) has been documented in the literature at 1.9–23.3% (3)
  • there are no known clinical or histological features that can help distinguish metastasising tumours from pleomorphic adenomas that do not recur and do not metastasise
  • haematogenous spread of pleomorphic adenoma is believed to be more common than lymphatic spread, as bones and lungs are the most obvious sites for metastasis
  • metastases of these benign pleomorphic adenomas are thought to be associated with intraoperative implantation of tumour cells through vascular or lymphatic routes (2)
    • therefore meticulous resection at the initial operation is important to prevent local recurrence and distant metastasis

Reference:

1. Al-Khateeb TH, Ababneh KT. Salivary tumors in north Jordanians: A descriptive study. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2007
2. Sabesan T et al.Metastasising pleomorphic adenoma of the parotid gland. Br J Oral Maxillofac Surg. 2007 Jan;45(1):65-7.
3. Ethunandan et al.Atypical features in pleomorphic adenoma--a clinicopathologic study and implications for management. Int J Oral Maxillofac Surg. 2006 Jul;35(7):608-12.