Salivary gland tumours may not be a common topic for health discussion but it is not an infrequent diagnosis in a neck lump for the unsuspecting patient. Fortunately, most of them are non-cancerous (benign). The parotid gland, which is the largest salivary gland in our body, is the most commonly afflicted site. 

Treatment for salivary gland tumours always begin with surgery to remove the tumour. The surgery needs to be thorough such that no cancer is left behind. Following that, several important information is obtained from the histology report. These include:

  • Whether it is benign or cancerous?
  • What histological type?
  • If cancerous, what grade of malignancy? Are the margins free of cancer?
  • Other high-risk features present? These suggest a poorer prognosis

The above information will determine whether the patient requires additional surgery or additional treatment such as radiation or chemotherapy.

Types of salivary gland tumours

Many different types of salivary gland tumours exist. These are classified according to the type of cells involved in the tumours. Knowing the type of salivary gland tumour helps us determine which treatment options are best for you.

Benign (non-cancerous) salivary gland tumours include:

  • Pleomorphic adenoma (most common)
  • Basal cell adenoma
  • Canalicular adenoma
  • Oncocytoma
  • Warthin tumour

Malignant (cancerous) salivary gland tumours include:

  • Acinic cell carcinoma
  • Adenocarcinoma
  • Adenoid cystic carcinoma
  • Clear cell carcinoma
  • Malignant mixed tumor (carcinoma ex-pleomorphic adenoma)
  • Mucoepidermoid carcinoma (most common)
  • Oncocytic carcinoma
  • Polymorphous low-grade adenocarcinoma
  • Salivary duct carcinoma
  • Squamous cell carcinoma
  • Undifferentiated carcinoma

 

 

Salivary cancers are given a grade (from 1 to 3, or from low to high), based on how abnormal the cancers look under a microscope. The grade gives a rough idea of how quickly it is likely to grow and spread.

  • Grade 1 cancers (also called low grade or well differentiated) look very much like normal salivary gland cells. They tend to grow slowly and have a good outcome (prognosis).
  • Grade 2 cancers (also called intermediate grade or moderately differentiated) have an appearance and outlook that is between grade 1 and grade 3 cancers.
  • Grade 3 cancers (also called high grade or poorly differentiated) look very different from normal cells and often grow and/or spread quickly. The outlook for these cancers is usually not as good as for lower grade cancers.

Other cancers that can affect the salivary glands

Typically, these not considered true salivary gland cancers, either because they usually arise in other parts of the body, or because they start elsewhere and then grow into or spread to the salivary glands.

Non-Hodgkin lymphoma: Most non-Hodgkin lymphomas start in lymph nodes. Rarely, these cancers start in immune system cells within the salivary glands. They behave and are treated differently from other types of cancers in the salivary glands. Most lymphomas that start in the salivary glands affect people with Sjogren syndrome (a disorder that causes the immune system to attack salivary gland cells). 

Sarcomas: The salivary glands contain blood vessels, muscle cells, and cells that make connective tissue. Cancers that start in these types of cells are called sarcomas but these occur very rarely in the salivary gland.

Secondary salivary gland cancers: Cancers that start elsewhere and spread to the salivary glands are called secondary salivary gland cancers. These cancers are treated based on where the cancer started. A common example is a type of skin cancer called squamous cell carcinoma (SCC) that spreads from the face or scalp to the parotid glands.

Treatment

Salivary gland surgery
As mentioned, treatment always begin with surgery to remove the tumour completely. This may involve the additional removal of adjacent structures that are involved such as nerves, skin and bone. When dealing with malignant tumours, surgery to remove the associated lymph nodes is necessary as they provide additional information on the stage of cancer. 

An experienced surgeon is important to ensure a complete removal of the tumour whilst minimizing complications. The most common complications are associated with the nerves that are in close contact with the salivary glands. In the case of the parotid gland, the facial nerve controls the facial muscles that have a functional importance and appearance. I routinely use a nerve monitor device during such operations to warn me of possible injury to these tiny nerve branches. 

Radiation therapy
Radiation therapy uses high-powered energy beams, such as X-rays and protons, to kill cancer cells. It can be used after surgery to kill any potential cancer cells that might remain. If surgery isn’t possible because a tumour is very large or is located in a place that makes removal too risky, radiation alone or in combination with chemotherapy may be recommended.

Chemotherapy
Unlike some types of cancers, chemotherapy isn’t given alone as a single treatment for salivary gland cancer. Chemotherapy may be an option for people with advanced salivary gland cancer in which case it is given in combination with radiation therapy.

Parotid gland tumour
Facial nerves left intact after removal of tumour
After parotid surgery

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