Salivary gland cancer

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ENT surgeon, Dr Mark Torres-Holmes, expands on salivary gland cancer and why a skilled surgeon is imperative to avoid nerve damage.

Function of salivary glands

We have both major and minor salivary glands secreting saliva into the mouth. The minor salivary glands are many, about 8000, and are single salivary units which open directly into the mouth, mostly situated on the inside lips, cheeks, hard and soft palates.

We call the major ones major because they are both bigger than the minor ones and made up of many salivary units which collect saliva into ducts which then open into the mouth. There are three pairs of these: the parotid gland in front of the ear; the submandibular gland under the jaw; and the sublingual gland under the tongue.

The minor salivary glands and submandibular glands are largely responsible for the saliva in your mouth at rest, when you’re not eating. The parotid gland works mostly when you eat and makes a different consistency of saliva than the submandibular glands.

Saliva helps to protect your teeth and prepare the food for chewing and swallowing. It also gets the digestive enzymes going. Like anything in the body, you don’t realise how important it is until you lose it.

Problems with the salivary glands are usually divided into inflammatory and neoplastic (tumour) causes, though rarely there are developmental masses also. The most common acute inflammatory causes are viral but sometimes bacterial infection, duct obstruction from scarring or stones, and immune-mediated inflammation. Chronic inflammatory causes are usually immune-mediated or auto-immune.

Salivary gland tumours

Eighty percent of salivary gland tumours occur in the parotid gland, 80% of these are non-cancerous and 80% are pleomorphic adenomas. Salivary tumours usually present as painless, slow-growing masses. The most common malignant primary neoplasms are adenoid cystic and mucoepidermoid carcinomas. Unfortunately, we don’t know the cause of salivary gland tumours. We almost always recommend excision of salivary neoplasms because even non-cancerous ones can transform into cancers.

Initial investigations for suspected tumours usually include an ultrasound, CT or MRI scan. MRI gives the best soft tissue definition for salivary neoplasms. We like fine needle aspiration biopsies (FNAB) to learn more about the nature of these tumours and to exclude other diseases like lymphomas or chronic infection. This helps for better decision-making and pre-operative counselling.

Skilled surgery

Major salivary gland surgery is essentially nerve surgery, meaning a critical aspect of the operation is identifying and preserving cranial nerves. Obviously, we need to get the whole tumour out without compromising the capsule, but it’s damage to nerves that causes morbidity.

This is another area where the skill and training of the surgeon comes into play. The most important nerve for the parotid gland is the facial nerve; for the submandibular gland it’s the marginal mandibular branch of the facial nerve as well as the lingual and hypoglossal nerves; and for the sublingual gland it’s the lingual nerve.

Adenoid cystic carcinomas

Adenoid cystic carcinomas are a high-grade neoplasm that has a propensity to invade and spread along nerves and therefore has a higher rate of local recurrence and/or distant metastasis, particularly to the lungs. Nodal metastasis is not common.

These tumours mostly occur in the major salivary glands and the minor salivary glands of the mouth but can also occur where there are other minor salivary glands, such as the nose and sinuses, pharynx, larynx or trachea.

The best chance of cure with these cancers is complete surgical excision preserving important structures. Due to the high grade of these tumours, sometimes close or positive margins, and their propensity for perineural invasion, post-operative radiation is almost always indicated to achieve local control.

The presence of metastasis to the lungs or bones at the time of diagnosis doesn’t preclude the value of good loco-regional control. Patients can live many years with metastasis but if it’s possible to remove these metastasis safely or give radiation to these sites, then long-term survival is more likely to be achieved.

As with all head and neck cancers, an individualised multi-disciplinary team approach will give the best outcomes.

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