Salivary gland cancer

If you’d like to know more about location and structure of the salivary glands, this information is in our section about head and neck anatomy.

There is a huge and bewildering range of salivary neoplasms (see Table 1), the majority of which (70 - 80 %) are benign and pleomorphic adenoma the most common of those.

**Table 1:** World Health Organisation classification of salivary neoplasms
Adenomas (benign tumours originating from epithelial (lining) tissue of the gland) Pleomorphic adenoma Myoepithelioma Basal cell adenoma Adenolymphoma (Warthin’s tumour) Oncocytoma Canalicular adenoma Sebaceous adenoma Ductal papilloma Cystadenoma Carcinomas (malignant tumours originating from epithelial (lining) tissue of the gland) Acinic cell carcinoma Mucoepidermoid carcinoma Adenoid cystic carcinoma Polymorphous low grade adenocarcinoma Epithelial-myoepithelial carcinoma Basal cell adenocarcinoma Sebaceous carcinoma Papillary cystadenocarcinoma Mucinous adenocarcinoma Oncocytic carcinoma Salivary duct carcinoma Adenocarcinoma (not otherwise specified) Myoepithelial carcinoma Carcinoma in pleomorphic adenoma Squamous cell carcinoma Small cell carcinoma Undifferentiated carcinoma Other carcinomas Nonepithelial tumours Malignant lymphomas Secondary tumours Unclassified tumours Tumour-like lesions Sialadenosis Oncocytosis Necrotising sialometaplasia Benign lymphoepithelial lesion Salivary gland cysts Chronic sclerosing sialadenitis of submandibular gland Cystic lymphoid hyperplasia of AIDS

Adenoid cystic carcinoma is the most common malignancy in the sublingual gland and in minor salivary glands. It is slow growing with local invasion and has a particular predilection for neural invasion. It may produce ‘skip’ lesions such that there may be tumour left in nerves beyond a histologically clear resection margin. There is a slight female preponderance and it presents most frequently in patients in their fifties. It has a characteristic ‘Swiss cheese’ pattern on histology although there are several histological variants. Less than 10 % of patients have cervical (neck) lymph node involvement at presentation and 30 % will get regional or distant metastases at some point, although this may be in the quite distant future. Pulmonary (lung) metastases are particularly frequent with this malignancy.

Mucoepidermoid carcinoma (made up of a mixture of mucus secreting cells and squamous (top layer of skin) cells) overall is probably the most common primary salivary gland malignancy. It presents in different grades of aggressiveness. There is an equal sex ratio, presentation is typically in the third to fifth decades and the majority of these tumours occur in the parotid glands. They are malignant but tend to behave in either a relatively indolent way, or an aggressively malignant way in which regional and distant metastases are common. Attempts to identify and separate these behaviours on histological grounds early have been the subject of controversy as 30 % of tumours that look like low-grade lesions histologically behave aggressively, and 30 % of those that appear high-grade lesions behave in a more benign fashion.

Acinic cell (secreting cells) carcinomas account for a minority of salivary gland tumours. 90 % of acinic cell carcinomas occur in the parotid glands. 80 % of these tumours are relatively indolent and 20 % are highly aggressive, but (much more so than for mucoepidermoid carcinoma; see above), the histology struggles to predict the tumour’s behaviour.

Carcinoma ex pleomorphic salivary adenoma is a highly malignant tumour that arises within a pre-existing pleomorphic salivary adenoma that has usually been present for many years. After about 10 years the incidence of malignancy in a pleomorphic salivary adenoma is about 1 % per year. Sudden growth, pain, facial nerve weakness or painful facial nerve palsy from tumour infiltration in a long-standing parotid lump are highly suggestive of malignant transformation.

Carcinoma ex pleomorphic salivary adenoma

is a rare, aggressive malignancy
is the most common of three types of malignant mixed tumours of salivary glands
male to female ratio is 2 : 1
occurs usually in older patients (6^th to 8^th decade) who have a pleomorphic adenoma in situ for many years (typically 10-15 years)
has an overall 5 year survival rate of 30 %
leads to regional metastasis in 50 % of patients
has a high rate of metastasis at the time of diagnosis (25 - 76 %), typically to brain, bone, lung and local lymph nodes.

Other malignancies such as mesenchymal tumours (soft / connective tissue tumours) or lymphoma may occur in the salivary glands. Secondary deposits (metastases) can occur and metastasis from a primary skin tumour to an intra-parotid node is the most frequent cause of a malignant parotid mass in areas of the world with a high incidence of cancer of the scalp. Polymorphous low grade adenocarcinoma (originating from tissue lining the gland) is worth remembering as it is frequently difficult to distinguish histologically but is generally an indolent malignancy with a good prognosis.

In addition, consideration should be given to malignant mixed salivary gland tumours. According to the World Health Organisation these are

carcinoma ex pleomorphic salivary adenoma (see above)
carcinosarcoma (a rare true mixed malignant tumour; almost always also arises from pre-existing pleomorphic salivary adenoma)
metastasising pleomorphic salivary adenoma (which remains something of a controversy).