What is Parotid Cancer?
Salivary gland tumours can either be harmless (benign) or harmful (malignant), and harmful tumours may either start in the salivary gland (primary) or spread from elsewhere (metastatic). The salivary gland is made up of different types of tissues (epithelial and non-epithelial), and so there are many possible types of salivary gland tumors. However, some of these types are quite rare. These tumors can be difficult to identify and can behave differently from case to case. Sometimes, it can be challenging to distinguish between different types of tumors, especially when using a diagnostic procedure called fine-needle aspiration (FNA).
An interesting aspect of salivary gland tumours is that the most common harmless tumor, the pleomorphic adenoma, has the potential to become harmful. Even though this tumor type is considered benign, it can come back after treatment. This variety of disease forms, signs, diagnosis challenges, and treatment options make salivary gland tumours a frequent topic in clinical examinations.
Harmful salivary gland tumours usually develop in people above 60 years, while harmless lesions are more common in people in their 40s and 50s. Women are more likely to have benign tumours, but harmful tumours occur equally in both males and females. Most salivary gland tumours are found in a gland in the cheek area, the parotid gland, with about 10% found in a gland under the lower jaw, the submandibular gland. Less than 4% of these tumors are found in smaller salivary glands around the mouth and throat. Usually, tumours found in the parotid gland are harmless, with the pleomorphic adenoma being the most common. However, tumours found in the submandibular and smaller salivary glands are more likely to be harmful.
The chance of death due to salivary gland tumours is based on how advanced the tumour is. On average, about 70% of patients survive for at least five years after diagnosis.
What Causes Parotid Cancer?
There are two main ideas about how salivary gland tumors start, but most experts agree with a theory that each kind of tumor comes from a specific type of cell within the salivary gland. In this theory, cells called excretory stem cells can turn into mucoepidermoid and squamous cell carcinomas, two kinds of cancer. Another type of cell, called intercalated stem cells, can turn into pleomorphic adenomas, adenoid cystic carcinomas, oncocytomas, adenocarcinomas, and acinic cell carcinomas, various types of tumors that can be cancerous.
Exposure to radiation has been linked to cancers in the parotid glands, part of the salivary glands, that show up 15 years after the exposure. Cigarette smoking and alcohol use have been connected to cancers in the head and neck, specifically, skin cancers in these areas can sometimes spread to the parotid glands. There have also been reports suggesting a link between exposure to silica dust and nitrosamines, chemical compounds found in many types of processed foods, and cancer.
However, it’s crucial to remember that alcohol use and smoking are not associated with tumors in the salivary glands, with the single exception of a type of tumor called Warthin tumor.
Risk Factors and Frequency for Parotid Cancer
Salivary glands usually develop non-cancerous conditions, while actual cancers are uncommon. In the UK, around 300 cases of salivary gland cancer get reported every year and less than ten of these are in children. People usually get diagnosed with this type of cancer in their sixties. Across the globe, about 0.5 to 3.0 people out of 100,000 get diagnosed with this cancer every year, making around 5% of all head and neck cancers. The survival rate for five years after being diagnosed depends on how advanced the cancer is when found, but it’s typically about 70%.
Signs and Symptoms of Parotid Cancer
A painless lump that grows slowly is a typical sign of a salivary gland mass. Symptoms like sudden growth, pain, skin changes, swollen neck glands, and facial weakness could suggest that the lump is cancerous. A lump near the bottom of the salivary gland could be mistaken for a swollen neck node. You’ll find bilateral lumps most commonly in certain conditions such as Warthin tumors and HIV-related growths. Parotid lumps can also be caused by infections, autoimmune conditions, or inflammation, which may be mistaken for tumors, making a thorough medical history vital.
People with a lump in their salivary gland should have it inspected and felt by a healthcare professional. There should also be an oral examination of the right salivary gland duct. For instance, the submandibular duct is on the floor of the mouth, while the parotid duct is opposite the second upper molar. Feeling around the mouth can help evaluate the lump’s extent, particularly with tumors in the submandibular gland. Clinicians should inspect the back of the throat for any signs of the lump spreading, which may show up as movement of the tonsil. A compulsory facial nerve evaluation and neck node palpation should also be done. If there’s facial weakness, this could indicate a cancerous lesion that’s invaded the nerve. Lastly, the skin on the head and neck should be examined for signs of cancer.
Testing for Parotid Cancer
If your doctor suspects you may have a disease of the salivary gland, they might use a procedure called Fine-Needle Aspiration Biopsy (FNA). This involves taking a sample of cells from your salivary gland using a thin needle. FNA is usually not painful and rarely has potential complications. However, interpreting the results can be complex and depends on the technique used in taking the sample, the quality of the sample obtained, and the expertise of the professional analyzing the cells. False positives can occur, which means sometimes, the test may suggest cancer when it is not actually present.
In such situations, it’s crucial to look at other pieces of evidence, such as your symptoms and results from other tests. If any of the test results contradict each other, your doctor will use their judgment and may ask for additional tests.
Besides FNA, your doctor may also use imaging methods to better understand what’s happening in your salivary gland. An ultrasound scan can offer important details about the size, position, and characteristics of the tumor and if it has spread to the lymph nodes in the neck. The ultrasound can also help guide the needle during an FNA procedure, which can improve the accuracy of the sample collection.
In uncomplicated, benign (non-cancerous) tumors, more sophisticated imaging methods like MRI may not be required. However, an MRI can be helpful in complex cases as it shows detailed images of the salivary gland and surrounding structures, including the facial nerve. This can be particularly useful in planning the treatment approach.
If your doctor suspects that cancer might have spread from the salivary gland to other parts of the body, they may recommend a specialized scan known as an F-18 fluorodeoxyglucose PET scan. A newer approach using a technetium scan has also been recently introduced to diagnose a type of salivary gland tumor known as Warthin tumors.
Treatment Options for Parotid Cancer
Benign Tumors in the Parotid Gland
Surgery is usually the preferred method for treating benign (non-cancerous) tumors in the parotid gland. These procedures, which are aimed at removing the gatekeeper salivary gland, can range from comprehensive to more focused approaches. A traditional surgery consists of exposing and identifying a facial nerve during a procedure known as a superficial parotidectomy. Nowadays, it’s often enough to remove the tumor itself and a small layer of healthy tissue around it (about 1 to 2 millimeters).
Some less invasive options include a partial parotidectomy or a hemi-superficial parotidectomy, which are surgeries removing only a part of the parotid gland. If a benign tumor is located away from the main branches of the facial nerve, it can be safely removed in an operation called an extracapsular dissection. In some cases, even endoscopic parotidectomy (a minimal invasive surgery with a camera and small tools) can be performed. However, comprehensive removal of the tumor, leaving no cancer cells behind, is crucial. A tumor might come back if the surgery was incomplete or if some cancer cells were accidentally spread during the operation.
Surgery complications can happen and may include a visible scar, injury to the facial nerve, internal bleeding (hematoma), a leak of the clear, straw-coloured fluid found in the body (seroma), a hole in the gland (fistula), and a condition causing excessive sweating when eating (Frey syndrome).
In cases where some tumor cells were accidentally spread during surgery, a long-term follow-up is recommended as the disease might come back. Radiation therapy is sometimes suggested as well but this depends on the individual patient’s circumstances.
Post-operative radiation therapy can be beneficial after a tumor recurrence but it can also prove challenging. The tumor can appear in multiple places and the facial nerve can be involved. Even though it’s best to avoid harming the facial nerve, sometimes it must be resected (cut away) during surgery. In these cases, postoperative radiation therapy might help reduce the chances of the tumor coming back.
Malignant Tumors in the Parotid Gland
In contrast, dealing with malignant (cancerous) tumors in the parotid gland often requires a more comprehensive approach. If the cancer is small and less aggressive, a simple superficial parotidectomy might be enough. However, if the tumor is larger or more aggressive, a full parotidectomy might be advised. This can sometimes even involve removing nearby neck structures.
If the facial nerve is infiltrated with the tumor, it might need to be removed. In these cases, primary nerve grafting, or using a healthy nerve to substitute the resected one, should be performed to maintain facial function.
When it comes to patients who show clinical or radiological signs of nodal disease (cancer spread to lymph nodes), a procedure called a neck dissection is recommended. This also applies to patients with high-risk tumors.
Lastly, salivary gland cells usually don’t respond well to chemotherapy. This method is, therefore, reserved for reducing symptoms in advanced stages of cancer. Radiation therapy is suggested after surgery in certain circumstances such as large tumor size or if the surgical margins (outer edges of the area where the tumor was removed) are too close. It’s also recommended for cases of cancer recurrence, cancer spread to nerves or blood vessels, cancer spread to lymph nodes, Advanced metastatic disease (cancer spread to other body parts), certain types of cancer, and high-grade tumors (cancer that looks very different from normal cells and grows quickly.)
What else can Parotid Cancer be?
When a doctor is examining a patient for certain types of cancer, they have to look at other conditions that might appear similar. Depending on the type of cancer, here are some conditions that they might consider:
They first consider Mucoepidermoid Carcinoma by ruling out the following conditions:
- Necrotizing sialometaplasia
- Pleomorphic adenoma with squamous metaplasia
- Sclerosing polycystic adenosis
Next, for Adenoid Cystic Carcinoma, they look at other possibilities:
- Pleomorphic adenoma
- Polymorphous adenocarcinoma
- Epithelial-myoepithelial carcinoma
- Basal cell adenocarcinoma
Finally, in cases of Acinic Cell Carcinoma, the following conditions might also be considered:
- Secretory carcinoma
What to expect with Parotid Cancer
The chances of living for at least five years after being diagnosed with salivary gland cancer are largely dependent on two things: the specific type of cancer cells (histological type), and how advanced the cancer is (the stage).
Across all types and stages of salivary gland cancer, the overall rate of survival over five years is 72%. However, the survival rates differ depending on the stage of the cancer when diagnosed:
* For those diagnosed with Stage I salivary gland cancer, the five-year survival rate is 91%. This means that out of 100 people, 91 will likely be alive five years after their diagnosis.
* For Stage II salivary gland cancer, the five-year survival rate is 75%. In other words, 75 out of 100 patients will still likely be alive after five years.
* For those diagnosed with more advanced cancer – Stage III or IV – the five-year survival rate can vary between 39% and 65%. This means that depending on factors like the specific type of cancer and their overall health, between 39 and 65 out of 100 patients can expect to live for at least five years after their diagnosis.
Preventing Parotid Cancer
Since there’s a chance that salivary gland cancer could come back or spread to other parts of the body, it is important for patients with a history of this disease to have regular checks throughout their life. As part of these follow-up appointments, ear, nose, and throat (otolaryngologist) specialists can provide tailored information about the likelihood of the cancer returning. Routine care may include blood tests or scans. However, the type of tests recommended will depend on the original type and stage of cancer and the treatments that the patient has received.
