Cancerous tumours of the salivary glands

A cancerous tumour of the salivary glands can grow into nearby tissue and destroy it. The tumour can also spread (metastasize) to other parts of the body.

Not many people develop salivary gland cancer. The following are the most common types of cancerous salivary gland tumours.

Mucoepidermoid carcinoma (MEC) is the most common type of salivary gland cancer. Most MEC tumours develop in the parotid glands, though some develop in the submandibular glands and minor salivary glands. It is the most common salivary gland cancer found in people over the age of 20.

MEC tumours are made up of 3 different cell types. They are called mucin-secreting, epidermoid and intermediate cells. The amount of each cell type found in a tumour can vary.

The different grades of MEC tumours have different characteristics:

Low-grade MEC is found more often in younger people and more frequently in women. These tumours are most often found at an early stage and have an excellent prognosis.

High-grade MEC is usually found in older people and more often in men. These tumours are more likely to spread to other parts of the body and are often diagnosed at later stages (3 or 4). This type of MEC has a poor prognosis.

Intermediate MEC has characteristics in between low-grade and high-grade MEC. Tumours are smaller than high-grade MEC, but they are often found when they have spread to the lymph nodes in the neck. Some people with intermediate MEC do as well as people with low-grade MEC, while others have a tumour that behaves more like a high-grade MEC. Research is looking for ways to identify what causes these different behaviours in intermediate MEC.

Adenoid cystic carcinoma is the second most common salivary gland tumour. While it can occur in almost any salivary gland, it is most often found in the minor salivary glands. They are more common in people between 40 and 60 years of age.

While adenoid cystic carcinoma doesn't usually spread to the lymph nodes near the tumour, it can grow along the space around the nerves (called perineural invasion) in the area around the tumour. It also spreads through the bloodstream to distant parts of the body. Adenoid cystic carcinoma can also come back (recur) many years after treatment.

Adenoid cystic carcinoma tumours can be made up of 3 different types of cells. Most tumours have 2 or 3 different types of cells in them. Adenoid cystic carcinoma is divided into types based on the cells in the tumour.

Solid adenoid cystic carcinoma tumours have cells that look like solid sheets when examined under a microscope. This type of adenoid cystic carcinoma has the worst prognosis among the 3 types.

Tubular adenoid cystic carcinoma tumours are made up of cells shaped like tubes. They have the best prognosis.

Cribriform adenoid cystic carcinoma tumours have cancer cells surrounded by normal cells. Under the microscope, the tumour sample looks like it has a lot of holes. Cribriform is the most common form of adenoid cystic carcinoma. These tumours have a prognosis in between the solid and tubular types.

Acinic cell carcinoma most often develops in a parotid gland. This type of salivary gland tumour is found in children and in adults around the age of 50. Most acinic cell carcinoma tumours are slow growing and have a good prognosis.

Salivary duct carcinoma is a high grade tumour that starts to grow suddenly and spreads quickly to the lymph nodes and other parts of the body. It often spreads along the space around the nerves (called perineural invasion). Most people are diagnosed at later stages of the disease, when the cancer has already spread. Salivary duct carcinomas are most commonly found in a parotid gland.

The following types of salivary gland tumours are rare.

Polymorphous low-grade adenocarcinoma is a very slow-growing tumour that almost always starts in the minor salivary glands. This cancer usually develops at the junction of the hard and soft palates. It rarely spreads to other parts of the body and does not come back very often.

Carcinoma ex-pleomorphic adenoma starts when the cells in a non-cancerous tumour called a pleomorphic adenoma change to cancer cells. Mammary analog secretory carcinoma is a slow-growing tumour that usually starts in a parotid gland. It can spread to the lymph nodes.

Rare salivary gland tumours are removed with surgery. A neck dissection may be done to check and remove lymph nodes. External radiation therapy may be given if the cancer has spread into the surrounding tissues or to the lymph nodes.