Salivary Gland Tumours

The salivary glands are paired as the parotid, submandibular and sublingual glands along with a large number of minor salivary glands. Tumours of the salivary glands may be benign or malignant.

• Neoplasms of salivary glands affect about 1 to 2 per 100,000.
• They are fewer than 1% of all cancers and 3 to 6% of all tumours of the head and neck.
• Tumours and are most common in the sixth decade of life.
• Malignancy typically presents after age 60, whilst benign lesions usually occur after 40.
• Benign tumours are more common in women, but malignant tumours have an equal sex distribution.
• 80% of tumours arise in the parotid glands, 10 to 15% in the submandibular glands and the rest in the sublingual and minor salivary glands.¹
  • 20% of parotid tumours are malignant
  • 50% of submandibular tumours are malignant
  • Most sublingual and minor salivary gland tumours are malignant.

• Radiation to the neck increases the risk of malignancy of salivary glands 15 to 20 years later.²
• Warthin tumours are more common in smokers. See below for more detail.

Symptoms

• Ask about the presentation of the mass, growth rate, changes in size or symptoms with meals, facial weakness or asymmetry, and associated pain. A general history may suggest possible inflammatory, infectious, or autoimmune causes.
• Most salivary gland neoplasms are a slowly enlarging painless mass. Parotid neoplasms most commonly occur in the tail of the gland as a discrete mass in an otherwise normal gland.
• Submandibular neoplasms often appear with diffuse enlargement of the gland, whereas sublingual tumours produce a palpable fullness in the floor of the mouth.
• Minor salivary gland tumours vary according on the site of origin. Painless masses on the palate or floor of mouth are the most common form but laryngeal salivary gland tumours can produce airway obstruction, dysphagia, or hoarseness. In the nasal cavity or paranasal sinus they cause nasal obstruction or sinusitis.
• Facial palsy with a salivary gland mass indicates malignancy. Pain can occur with both benign and malignant tumours. Pain may arise from suppuration or haemorrhage into a mass or from infiltration of adjacent tissue.

Signs

• Note the size and mobility of the mass, as well as any fixation to local structures and any tenderness.
• Note skin and mucosa in sites which drain to the parotid and submandibular lymphatics. Regional metastases from skin or mucosal malignancies may present as salivary gland masses.
• Neurological examination of the cranial nerves may reveal neural infiltration in malignant lesions.

• Pleomorphic adenoma, also called benign mixed tumour is the commonest tumour of the parotid gland and represents about 60% of cases. It is also 36% of submandibular tumours. They are slow-growing and asymptomatic.
• Mucoepidermoid carcinoma is the commonest malignancy of the parotid gland and is the 2nd commonest of the submandibular gland after adenoid cystic carcinoma. It represents about 8% of all parotid tumours. Adenocarcinoma represents 2 or 3% of salivary tumours. Acinic cell carcinoma is a low-grade neoplasm that represents 1% of all salivary gland neoplasms. 95% arise in the parotid gland.
• In children most parotid tumours are benign and are haemangiomas but malignancy does occur although prognosis is often good.³
• Warthin tumours are the 2nd commonest benign salivary gland neoplasm, representing about 6 to 10% of all parotid tumours. They rarely occur in other glands and 12% are bilateral. They are 8 times as common in smokers as non-smokers and are unique amongst tumours of smokers in that they are not malignant. They present most often in the 6th decade in women and the 7th decade in men.⁴
• Occasionally lymphoma can present in a salivary gland

• Imaging studies of the salivary glands are usually unnecessary for small tumours of the parotid or submandibular gland. CT or MRI is useful to assess large tumours and for evaluating any extension beyond the gland. It may also be helpful for evaluation of cervical lymph nodes for metastasis.
• Minor salivary gland neoplasms are often difficult to assess on examination, and the use of preoperative CT or MRI is important.
• CT-guided needle biopsy guided can be used.

This staging system⁵ is based on tumour size, local extension, cervical lymph node metastases, and distant metastases and it correlates with survival. There is a significant difference in outcome between low and high grade malignancies.⁶

Non-Drug

Radiotherapy may play a part in the treatment of malignancy but the main line is surgery.

Drugs

Chemotherapy is usually with doxyrubicin or cis-platinum but response is poor.

Surgical

• Superficial parotidectomy with careful dissection of the facial nerve is required for diagnosis and treatment of a parotid mass. If it is malignant a more radical procedure sacrificing the facial nerve may be required but this should not be done before malignancy is confirmed. Complete excision of tumours in other salivary glands is required.
• Fine needle aspiration and biopsy (FNAB) of submandibular masses⁷ helps to exclude inflammatory disease, which is treated conservatively, or metastatic disease, which is treated on the basis of the primary tumour.
• Benign neoplasms of the submandibular gland require complete excision of the gland. Malignant neoplasms require complete excision with some extension.
• Up to 60% of patients with malignant minor salivary gland tumors of the larynx will develop recurrent disease locally, regionally, or at distant sites. Because of the high risk of recurrence, total laryngectomy is usually recommended.⁸

• Skilled dissection in a superficial parotidectomy is required to avoid damage to the facial nerve but repeat operations are much more likely to damage it. Complete excision of pleomorphic adenomas is important because recurrent tumours are often multifocal and may present 10 to 15 years later. Cure rates for recurrence are 25% or less. Radiotherapy may be helpful here.
• Pleomorphic adenomas can undergo malignant change and are called carcinoma ex-pleomorphic adenoma. They represent about 2 to 4% of salivary gland malignancies. The rate of malignant change increases with long-term observation beyond 10 years. Sudden rapid growth of a previously stable mass is typical. They are aggressive and have a poor prognosis.
• Frey's syndrome can occur after parotid surgery. The autonomic nerves reform inappropriately so that parasympathetic impulses go to sympathetic nerves. Hence stimulus to salivation will make the face sweat.
• Follow up of patients who have had parotidectomy for benign or malignant disease shows remarkably little adverse effect on the quality of life.⁹

The 10-year survival rate for parotid tumours is:

• Stage I 83%
• Stage II 76%
• Stage III 32%

Where there is facial nerve paralysis the 5 years survival rate is 9%.

Malignancies of the minor glands are rare but tend to have a good outcome.¹⁰

Carcinoma of the salivary duct is very rare but of low malignancy and with good outcome.¹¹

Tumours in children and adolescents are often malignant but the prognosis tends to be good.¹²

Because theses tumours are rare, there is a shortage of good clinical trials.¹³ Given the suboptimal response rates, duration of response, and toxicity of conventional chemotherapy, a better understanding of the biology of salivary gland malignancies will lead to improved understanding of prognosis and better treatment. With the emergence of molecular targeted therapy, these tumours become an optimal candidate for trials of investigational drugs and established drugs for new indications.¹⁴