Salivary gland cancer (SGC) is an uncommon malignancy that develops in the glands responsible for producing saliva. These tumors originate in the parotid, submandibular, sublingual, or the hundreds of minor salivary glands found throughout the upper aerodigestive tract. SGC accounts for a small fraction of all cancers, typically 3% to 5% of head and neck cancers. Although several risk factors have been identified, the precise cause for most cases remains unknown and is likely the result of multiple interacting factors.
Inherent Risk Factors
The risk of developing salivary gland cancer is strongly correlated with age, increasing significantly as individuals get older. Most diagnoses occur in older adults, typically after the age of 50, with the majority of patients being in their 50s or 60s. This suggests that the accumulation of cellular damage over a lifetime may contribute to tumor development.
Gender also presents a statistical difference in incidence, as the disease is slightly more frequently observed in men than in women. This difference represents a population-level trend, and the incidence can vary depending on which specific gland is affected.
A family history of salivary gland cancer may slightly increase an individual’s risk, suggesting a possible genetic component. This includes the possibility of uncommon inherited syndromes that predispose individuals to various cancers. However, the vast majority of these tumors arise without any clear genetic predisposition or strong family link.
Environmental and Occupational Exposures
Exposure to ionizing radiation is considered the most significant environmental factor linked to salivary gland cancer. Specifically, therapeutic radiation delivered to the head and neck area for prior medical conditions greatly increases the long-term risk. This exposure often occurred during treatment for other cancers, such as Hodgkin lymphoma or thyroid cancer.
The connection is particularly strong for patients who received high-dose radiation treatments decades ago, such as those administered before 1955. The risk can remain elevated for 20 years or more following the initial treatment. In contrast, the risk associated with low-dose diagnostic imaging, like modern dental X-rays, is considered weak or non-existent.
Certain workplace environments present risks due to exposure to specific toxic substances. Studies have identified an elevated risk for individuals working with nickel compounds or alloys, particularly nickel alloy dust. Employment in the rubber manufacturing industry has also been associated with higher rates of salivary gland cancer.
Other Occupational Risks
Other occupational exposures linked to increased risk include:
- Working with silica dust.
- Asbestos mining operations.
- Certain types of woodworking.
- Exposure to solvents and formaldehyde in the workplace.
- Professions such as plumbing, which may involve exposure to various heavy metals and industrial materials.
Pre-Existing Conditions and Lifestyle Links
A small fraction of salivary gland cancers arises from a transformation within a pre-existing, non-cancerous tumor. The most common example is the malignant change of a benign tumor, the pleomorphic adenoma, which can evolve into carcinoma ex pleomorphic adenoma. This transformation is rare, but it demonstrates a slow, multi-stage development process for some tumors.
Certain viral infections have been linked to an increased risk of developing specific types of salivary gland tumors. These include the Epstein-Barr virus (EBV), human immunodeficiency virus (HIV), and human papillomavirus (HPV). While an association exists, it is not fully understood if these viruses directly cause the cancer or if they contribute to a weakened immune environment that allows the cancer to develop.
Compared to other head and neck cancers, the link between common lifestyle factors like tobacco use and alcohol consumption and salivary gland cancer is less definitive. While smoking is a major risk factor for many cancers in the region, its association with malignant salivary gland cancer is often weak or inconsistent. However, smoking is strongly connected to an increased risk of developing Warthin tumor, a benign tumor of the salivary gland.
For heavy alcohol consumption, some studies suggest an elevated risk, but the data has not been consistently conclusive. Similarly, dietary factors, such as a diet low in vegetables and high in animal fat, have been suggested as a possible link, but more research is needed.