We learn about the different types of salivary gland tumours, both benign and malignant.
Salivary gland tumours are rare cancers in the head and neck region. They can develop in any of the different sub-regions of the head and neck, with the most frequent (80-85%) encountered in the parotid. The parotids are the largest of the salivary glands, located just in front and below the ears. Parotid gland tumours are often benign (non-cancerous) (75%). Tumours arising from the submandibular gland, sublingual gland, or the minor salivary glands are usually more likely to be malignant (cancerous).
The most common type of benign salivary gland tumour is a pleomorphic adenoma. This is typical painless and mobile, although the mobility can be compromised if the tumour becomes bigger. Rarer benign tumours include Warthin tumours (association with smokers), basal cell adenoma, and canalicular adenoma.
The most common malignant salivary gland tumours are mucoepidermoid carcinomas and adenoid cystic carcinomas.
Epidemiology and risk factors
Salivary gland tumours represent 6-8% of head and neck tumours. It’s more common in males and usually presents between the ages 50 and 60. Currently, no single factor has been identified as the cause. Although an association with certain factors plays a role. These include:
- Viral infections (Ebstein-Barr Virus, HIV, HPV)
- Previous radiation
- History of previous skin cancer
- Exposure to toxins in the workplace
Recent research suggests that people are more likely to develop salivary gland cancer if they have exposure to:
- Certain metals, such as nickel alloy dust
- Certain minerals, including silica dust
- Asbestos mining
- Plumbing equipment
- Rubber manufacturing
- Certain types of woodworking
Clinical presentation and imaging studies
Typical presentation depends on which salivary gland is affected.
Minor salivary glands
Painless/painful swelling in front or below ear.
Painless swelling under jaw.
Painless swelling under tongue.
Painless swelling – most common of the palate, cheek (inside), and lips.
Facial weakness with inability to close the eye and/or weakness with smiling (usually indication of cancerous growth).
Ulceration of the mucosa of palate, cheek (inside) and lips.
The significance of tumours in the parotid region is the close relation to the facial nerve. The facial nerve is one of the twelve cranial nerves supplying the facial muscles of expression. This nerve is transecting the salivary gland and a tumour can develop on top of, or underneath the nerve.
Physical examination stays the most important part of screening, followed by imaging studies. These include magnetic resonance imaging (MRI), computed tomography (CT) and sonar.
The difference in these modalities is the kind of tissue being evaluated. MRI provides more superior detail to soft tissue, comparing to CT being the choice if bony involvement is questioned (i.e. the jaw being infiltrated). CT imaging, however, can be used alone for soft tissue imaging as well.
Depending upon the location and size of a mass, ultrasound may also provide high-quality detail, being more cost-effective. Ultrasound, however, can be limited by big tumours and trying to assess the deep part of the parotid salivary gland. Ultrasound is also not as useful as other modalities for planning surgical treatment.
Controversy exists with obtaining tissue samples, especially with risk of injury to the facial nerve.
Cancers of the major glands are staged according to the TNM system. T refers to the size of the tumour, N to the involvement of lymph glands and M, indicating the presence of spread to other parts of the body.
There are several ways depending on location, staging, and the type of cancer.
• Surgery to remove the cancer.
Complete surgical resection is the cornerstone of treatment. Depending on the final type (pathological classification) of the tumour, surgery is sufficient with no further treatment.
The standard operation for tumours of the parotid is a parotidectomy, with removal of the superficial part of the parotid together with the tumour (depending on the location of the growth to the nerve). The most critical part is preservation of the facial nerve. Intra-operative facial nerve monitoring can be used as an aid, during this procedure.
• Radiation therapy (RT) and chemotherapy
RT is used in combination with surgery in certain cancerous tumours. Unresectable tumours may be treated with RT alone or RT in combination with chemotherapy.