Salivary Gland Tumors: Benign and Malignant

Salivary gland tumours are neoplasms arising from the epithelial and myoepithelial cells of the major and minor salivary glands. They form one of the most histologically diverse families of human tumours, ranging from common benign lesions such as pleomorphic adenoma to a wide variety of carcinomas, and are classified by the World Health Organization on the basis of their distinct histological types.

Definition

Salivary gland tumours are benign or malignant neoplasms of salivary epithelial and myoepithelial origin, grouped by the World Health Organization into distinct histological entities such as pleomorphic adenoma, Warthin tumour, mucoepidermoid carcinoma, and adenoid cystic carcinoma.

Scope

This topic covers the benign-malignant spectrum of salivary neoplasia: the main benign tumours, the principal carcinomas, the relationship between tumour site and the probability of malignancy, and the role of the WHO histological classification. It is a reference and educational overview of tumour categories and does not provide diagnostic or treatment guidance.

Core questions

• How does the probability of malignancy vary between the parotid, submandibular, sublingual, and minor glands?
• What are the most common benign and malignant salivary tumours?
• Why are salivary tumours regarded as histologically diverse?
• How does the WHO classification organise this diversity into defined entities?

Key concepts

• WHO histological classification of salivary tumours
• Pleomorphic adenoma
• Warthin tumour (papillary cystadenoma lymphomatosum)
• Mucoepidermoid carcinoma
• Adenoid cystic carcinoma
• Site-dependent malignancy risk
• Histological grading of salivary carcinomas

Mechanisms

Salivary glands contain several epithelial and myoepithelial cell populations, and tumours recapitulate this cellular diversity, which underlies the unusually large number of recognised histological entities. Pleomorphic adenoma, the most common benign tumour, shows a characteristic mixture of epithelial and stromal (myxoid, chondroid) elements. Among carcinomas, mucoepidermoid carcinoma combines mucous and epidermoid cells and is graded by histological features, while adenoid cystic carcinoma is notable for a cribriform pattern and for perineural invasion. Recurrent chromosomal translocations and fusion genes have been identified in several salivary tumour types, refining their classification.

Clinical relevance

A salivary gland tumour typically presents as a slowly enlarging, painless mass, and its location and histology determine whether it is benign or malignant, making accurate categorisation central to head and neck pathology. This entry describes how the tumours are classified and recognised for educational purposes and is not a basis for individual diagnostic or treatment decisions.

Epidemiology

Salivary gland tumours are uncommon relative to other head and neck neoplasms, and the large majority arise in the parotid gland, where most are benign; pleomorphic adenoma is the single most frequent tumour overall. The proportion that is malignant rises progressively from the parotid to the submandibular, sublingual, and minor glands. Mucoepidermoid carcinoma is generally the most common salivary malignancy, with adenoid cystic carcinoma also frequent, particularly in minor and submandibular glands.

History

Systematic histological classification of salivary tumours developed through the twentieth century, supported by large institutional case series such as the review of 2410 tumours by Eveson and Cawson, which documented the distribution of histological types by site, age, and sex. The World Health Organization classifications, refined across successive editions, established the internationally used framework of defined entities, and molecular studies have since identified recurrent gene fusions that characterise several tumour types.

Seminal works

• seethala-who-2017
• eveson-cawson-1985

Frequently asked questions

Are most salivary gland tumours benign or malignant?

Overall most are benign, especially in the parotid gland, where the majority of tumours are benign; however, the likelihood that a tumour is malignant increases in the submandibular, sublingual, and minor salivary glands.

What is the most common benign salivary gland tumour?

Pleomorphic adenoma is the most common benign salivary gland tumour and the most frequent salivary tumour overall, arising most often in the parotid gland.