Salivary Gland Tumour

Salivary gland tumours, also known as mucous gland adenomas or neoplasms, are tumours that form in the tissues of salivary glands. These glands are classified as major (parotid, submandibular, and sublingual) or minor (800 to 1000 small mucus-secreting glands located throughout the oral cavity lining). Patients with these tumours may be asymptomatic.

Presentation

Salivary gland tumours usually present as a lump or swelling in the affected gland, which may or may not have been present for a long time. This lump may be accompanied by symptoms of duct blockage, such as xerostomia. In the early stages, it is often challenging to distinguish between benign and malignant tumours. Malignant growths often exhibit nerve involvement, such as facial nerve damage leading to facial palsy. Other red flag symptoms include facial pain, paraesthesia, fixation of the lump to the overlying skin, ulceration, and induration of the mucosa.

Diagnosis

Several diagnostic methods can be used to determine the type of salivary gland tumour and its malignancy status:

• Physical Exam and History: Examining the head, neck, mouth, and throat for signs of disease, and taking a history of the patient's health habits and past illnesses.
• Endoscopy: A procedure involving the insertion of an endoscope into the mouth to view the mouth, throat, and larynx.
• MRI or CT Scan: These imaging tests can confirm the presence of a tumour and show whether metastasis has occurred.
• Biopsy: Removal of cells or tissues for microscopic examination by a pathologist.
• Fine Needle Aspiration (FNA) Biopsy: Removal of tissue or fluid using a thin needle, commonly used for salivary gland cancer.
• Radiographs: An orthopantomogram (OPG) can rule out mandibular involvement, and a chest radiograph can rule out secondary tumours.
• Ultrasound: Used to assess superficially located tumours in the submandibular or parotid gland.

Classification

The World Health Organisation's 2005 classification system is widely used and defines salivary gland neoplasms based on whether they are primary or secondary, benign or malignant, and by tissue of origin. The five broad categories include:

Benign Epithelial Tumours

• Pleomorphic adenoma
• Warthin's tumour
• Myoepithelioma
• Basal cell adenoma
• Oncocytoma
• Canalicular adenoma
• Lymphadenoma (Sebaceous and Nonsebaceous)
• Ductal papilloma (Inverted, Intraductal, Sialadenoma papilliferum)
• Cystadenoma

Malignant Epithelial Tumours

• Acinic cell carcinoma
• Mucoepidermoid carcinoma
• Adenoid cystic carcinoma
• Polymorphous low-grade adenocarcinoma
• Epithelial-myoepithelial carcinoma
• Clear cell carcinoma, not otherwise specified
• Basal cell adenocarcinoma
• Sebaceous carcinoma
• Sebaceous lymphadenocarcinoma
• Cystadenocarcinoma
• Low-grade cribriform cystadenocarcinoma
• Mucinous adenocarcinoma
• Oncocytic carcinoma
• Salivary duct carcinoma
• Salivary duct carcinoma, not otherwise specified
• Adenocarcinoma, not otherwise specified
• Myoepithelial carcinoma
• Carcinoma ex pleomorphic adenoma
• Mammary analogue secretory carcinoma
• Carcinosarcoma
• Metastasizing pleomorphic adenoma
• Squamous cell carcinoma
• Large cell carcinoma
• Lymphoepithelial carcinoma
• Sialoblastoma

Other Tumours

• Soft Tissue Tumours: Hemangioma
• Hematolymphoid Tumours: Hodgkin lymphoma, Diffuse large B-cell lymphoma, Extranodal marginal zone B cell lymphoma
• Secondary Tumours: Tumours metastasized from distant locations

Treatment

Treatment for salivary gland tumours often involves a combination of surgery, radiotherapy, and chemotherapy:

• Surgery: Complete surgical resection with adequate free margins is the mainstay treatment for salivary gland tumours.
• Radiotherapy: Used for cancerous tumours, either alone or in combination with surgery. Fast neutron therapy has shown significant effectiveness for unresectable tumours.
• Chemotherapy: Generally reserved for palliative treatment of symptomatic locally recurrent and/or metastatic disease. Conventional chemotherapy regimens include cisplatin and 5-FU or CAP (cisplatin, doxorubicin, and cyclophosphamide).

Targeted Therapy

Due to poor results with chemotherapy, novel therapeutic interventions are being looked at. Targeted agents like imatinib, cetuximab, gefitinib, and trastuzumab are under investigation, though the rarity of salivary gland tumours limits the available data.

Epidemiology

Salivary gland tumours are mostly benign (65-70%). Approximately 75-80% of parotid gland tumours and around 50% of submandibular gland tumours are benign. However, sublingual gland tumours are rare and often malignant. Ionising radiation has been reported as a causal factor for mucoepidermoid carcinoma. In the United States, the incidence rate of salivary gland cancers between 2009 and 2013 was 1.7 in 100,000.

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Self-assessment MCQs (single best answer)

Which salivary gland is most commonly affected by tumours?

What is a common presentation of salivary gland tumours?

Which imaging technique is most useful for confirming the presence of a salivary gland tumour?

Which type of biopsy is commonly used for diagnosing salivary gland cancer?

What is the most common type of benign salivary gland tumour?

What is a distinguishing feature of malignant salivary gland tumours?

Which treatment method is considered the mainstay for salivary gland tumours?

Which type of salivary gland tumour is often malignant?

Which novel therapeutic intervention is being looked at due to poor results with conventional chemotherapy?

What is the incidence rate of salivary gland cancers in the United States between 2009 and 2013?