Epidemiology
An uncommon tumour of the salivary glands; it makes up 10% of epithelial tumours; they make up a larger proportion of tumours which arise from minor salivary glands (30%). It is more common over the age of 40.
Natural History
Usually slow growing, but often invades neural structures and bone. The tumour frequently recurs following treatment. The long term outlook is poor with 90% of patients dying from disease within 15 years. Lymph nodes are uncommonly involved. Distant metastasis occurs in up to 50% of patients, usually to the lung.
Clinical Presentation
Symptoms are related to the mass or due to perineural invasion (pain or neuropathy). Cranial nerve examination is vital.
Tumour Features
The macroscopic findings are usually of a light coloured tumour with invasive margins. Microscopic appearances typically conform to one of three types. A mix of these is present in most tumours.
- Cribriform pattern is most common, with microcystic spaces containing mucoid material
- Tubular pattern mimics the tubular structure of the salivary glands, with a bilayered epithelium containing luminal ductal cells and outer myoepithlial cells.
- Solid pattern contains large clusters of basaloid cells.
Perineural invasion may be extensive and distant to the primary site. Ki-67 staining can identify mitotically active lesions from more benign tumours.
