Salivary gland cancer
Salivary gland cancer is a rare form of cancer that originates in the glands responsible for producing saliva, located in the mouth, nose, sinuses, and larynx. The majority of salivary gland tumors are benign, but when malignant, they can be classified into various types, with the parotid glands being the most commonly affected. Key risk factors include exposure to radiation in the head and neck region, certain workplace exposures, and tobacco use. Symptoms often manifest as a lump in the face, neck, or mouth, and can include pain or numbness. Diagnosis typically involves physical examinations and imaging tests such as MRI or CT scans, followed by a biopsy to confirm malignancy. Treatment varies by stage, with early-stage cancers usually addressed through surgical removal, while advanced cases may require radiation or chemotherapy. Prognosis is generally favorable for low-grade, slow-growing tumors, but the outcomes are less optimistic for high-grade tumors diagnosed at a later stage. Preventive measures include minimizing radiation exposure and avoiding tobacco products.
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Subject Terms
Salivary gland cancer
ALSO KNOWN AS: Parotid gland cancer
RELATED CONDITIONS: Throat, neck, and mouth cancers
DEFINITION: Salivary gland cancer develops in the glands that secrete saliva in the mouth, nose, sinuses, and larynx (voice box).
Risk factors: The main risk factor for developing salivary gland cancer is exposure to radiation in the head and neck. This exposure often occurs for other medical conditions. Workplace exposure to certain metals and silica dust also increases the likelihood of developing salivary gland cancer. Tobacco use increases the risk of developing squamous cell salivary gland cancer as well as squamous cell cancers of the throat and mouth. A few studies suggest that a diet high in animal fat and low in vegetables or a family history of salivary gland cancer are risk factors. Still, the studies have not been conclusive, and these risk factors appear minor compared with radiation exposure.
Etiology and the disease process: The salivary glands produce saliva that contains enzymes to help digest food. There are three pairs of major salivary glands. The largest are the parotid glands in front of and below each ear. The paired sublingual salivary glands are under the tongue, and the submandibular salivary glands are below the jawbone. There are also between six hundred and one thousand microscopic glands, called minor salivary glands, located in the mouth, nose, sinuses, and larynx lining.
About 70 to 80 percent of all salivary tumors develop in the parotid glands, and a smaller percentage develop in the submandibular glands. Most tumors in the salivary glands are benign (not cancerous). Tumors that begin in the minor salivary glands are usually malignant (cancerous). Malignant tumors are classified as low grade if they grow slowly and high grade if they grow aggressively and rapidly.
Salivary glands contain several types of cells, each giving rise to a different kind of tumor. About a dozen specific types of cancer can develop in these glands, and there are four major types of salivary gland cancer.
Mucoepidermoid carcinomas usually develop in the parotid glands. They may form low-grade or high-grade tumors. Acinic cell carcinomas also start in the parotid gland. They typically grow slowly but also tend to invade surrounding tissues. Adenoid cystic carcinomas are low-grade but persistent tumors that often cause the cancer to recur after surgery. Polymorphous low-grade adenocarcinomas usually begin in the minor salivary glands and grow slowly.
Other rare or very rare malignant carcinomas can develop in the salivary glands. Sebaceous adenocarcinoma, oncocytic carcinoma, and salivary duct carcinoma tend to have the worst outcomes. Basal cell adenocarcinomas, clear cell carcinomas, cystadenocarcinomas, and mucinous adenocarcinomas tend to be curable or have good outcomes. Other rare salivary gland cancers include squamous cell carcinoma, undifferentiated carcinomas, and mixed malignant carcinomas, all of which tend to be high-grade, aggressive cancers.
Incidence: Salivary cancer is rare, as most tumors in the salivary glands are benign. Three people per 100,000 people develop salivary gland cancer in the United States each year, mainly in the parotid gland. Most people are first diagnosed with salivary gland cancer between the ages of fifty and seventy, although this cancer occasionally can develop in children and young adults.
Symptoms: Salivary gland cancer often shows no symptoms in its early stages. The most common symptom is a lump on the face, neck, or mouth. Other symptoms include pain in these areas and numbness or weakness on one side of the face. These symptoms can also result from other conditions unrelated to salivary gland cancer.
Screening and diagnosis: Although there is no specific screening for salivary gland cancer, many cases are first detected during routine dental examinations. Diagnosis begins with a complete physical examination and patient history, followed by imaging scans. These may include magnetic resonance imaging (MRI) and a computed tomography (CT) or computed axial tomography (CAT) scan. These scans help provide a three-dimensional view of soft tissue within the body. An ultrasound helps to pinpoint tissue of different densities and helps locate the tumor. A positron emission tomography (PET) scan uses a small amount of radioactive glucose (sugar) to find tumors. Malignant cells divide faster than healthy cells and use more glucose, making them bright spots on the scan. Diagnosis is confirmed by a fine needle aspiration biopsy, in which a tissue sample is removed and examined for malignant cells under a microscope.
Salivary gland cancer is staged using the TNM system where T stands for the size of the tumor, N stands for the degree to which the cancer has spread to the nearby lymph nodes, and M stands for whether the cancer has spread (metastasized) to distant sites. The stages of salivary gland cancer are as follows:
- Stage 1: The tumor is less than 2 centimeters (cm) in diameter and has not spread to nearby tissue, lymph nodes, or distant sites.
- Stage II: The tumor is larger than 2 cm but less than 4 cm and has not spread to nearby tissue, lymph nodes, or distant sites.
- Stage III: The tumor is larger than 4 cm or has grown into nearby tissue but has not spread to the lymph nodes. Alternately, a tumor of any size that has spread to lymph nodes on the same side of the neck as the tumor is considered Stage III.
- Stage IV: The tumor is of any size but has invaded nearby structures (bones, skin, and so on) and lymph nodes or has spread to distant sites.
Treatment and therapy: Treatment depends on the cancer stage and the patient's health. Surgery is generally recommended for Stage I, II, and III salivary gland cancer. For Stage I, the cancer and the salivary gland are usually removed. For Stage II, the surgeon removes more facial tissue and may remove some lymph nodes in the neck on the same side as the tumor. For Stage III cancer, the tumor, some tissue, and lymph nodes on both sides of the neck are removed. Surgery may damage nerves in the face and neck. This may cause difficulty eating and speaking and can be disfiguring.
Radiation therapy is usually done after surgery, especially if the cancer cannot be completely removed. Chemotherapy is sometimes done after Stage III surgery, although this is not yet standard procedure. Stage IV cancer can rarely be cured. Radiation therapy and drugs are used to relieve pain and improve quality of life. Some experimental chemotherapy may be used.
Prognosis, prevention, and outcomes: Most tumors in the salivary glands are not cancerous. Malignant tumors of the salivary gland make up 0.5 to 1.2 percent of all tumors and about 5 percent of all head and neck cancers. Whether a salivary gland cancer can be cured depends on the cancer's cell type, whether the tumor is high or low grade, and the degree to which the cancer has invaded nearby tissues or spread to other parts of the body. The best outcomes are associated with slow-growing, low-grade tumors that are diagnosed early. The worst outcomes are associated with late-stage aggressive high-grade tumors. Overall five-year survival rates for all salivary gland cancers by stage are Stage I, 91 percent; Stage II, 75 percent; Stage III, 65 percent; and Stage IV, 39 percent.
To prevent salivary gland cancers, one should avoid unnecessary radiation exposure to the head and neck and workplace exposure to nickel alloy dust, silica dust, and similar fine metal or mineral dust. Avoiding all tobacco products also helps reduce the risk of squamous cell salivary gland cancer.
Bibliography
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