Cancer of the oral cavity occurs when malignant tumors are found in the tissues of the lip or mouth.  More than 90 percent of cancers of the oral cavity occur in the squamous cells that line the mucosal surfaces in the mouth and throat. In the oral cavity, these include the:

• Lips
• Inside lining of the cheek (buccal mucosa)
• Front two–thirds of the tongue
• Floor of the mouth
• Upper and lower gums (gingiva)
• Bony roof of the mouth (hard palate)
• Area behind the wisdom teeth (retromolar trigone)

Cancer cells develop because of damaged DNA, the genetic code that controls how cells behave. In most cases, when the DNA becomes damaged, the body is able to repair it. In cancer cells, the DNA is not repaired and the abnormal cells grow out of control. 

There are many types of tissues in the oral cavity composed of a variety of cells. Different types of cancer can develop from each kind of cell.  Most oral cancers start in the squamous cells, which are flat, scale–like cells that line the oral cavity. For this reason, oral cancer is often called squamous cell carcinoma. The type of cancer that develops is important as it determines the plan of treatment and the outlook for recovery.

Many types of tumors can develop as the result of oral cancers, and many of them are not malignant. Tumors that are benign do not spread to other tissues or parts of the body. Cancerous tumors, however, can penetrate the surrounding tissues and metastasize to other parts of the body. If lip and mouth cancers are not treated, they can spread to the:

• Pharynx. Tube that is part of the digestive tract and runs behind the nasal cavities, mouth and larynx.
  
  
• Larynx (voice box). Cartilage in the throat that houses the vocal cords. It connects to the lower pharynx.
  
  
• Esophagus. Tube that extends from the lower pharynx to the stomach. Food passes from the mouth through the pharynx and into the stomach.
  
  
• Thyroid gland. Located in the front of the neck, this gland contributes to hormone production.

Oral cancers occur more often in African Americans than whites and men have twice the risk than women. Men over the age of 40 are also at higher risk. More than half of all patients diagnosed with oral and oropharyngeal cancer are over the age of 65. Researchers believe the higher incidence of oral cancer cases in older individuals and males is linked to increased tobacco and alcohol use with these populations.

The number of new cases of oral cancer has been declining during the past 30 years. According to the Surveillance Epidemiology and End Results (SEER) cancer review published by the National Institutes of Health (NIH), the incidence of oral and oropharyngeal cancer in the United States dropped 1.8 percent between 1981 and 2004. In addition, the death rate for oral and oropharyngeal cancer decreased significantly since the late 1970s, with the fastest decline in the 1990s.

The American Cancer Society (ACS) estimates that 34,360 cases of oral and oropharyngeal cancer will be diagnosed in the United States in 2007. About half of these cancers will develop on the tongue and lips. Cancers on the floor of the mouth and in the minor salivary glands account for another 25 percent of these cancers. The remaining cancers are diagnosed in the gums and other areas of the mouth. The ACS estimates that about 7,500 people will dies of oral cancers in 2007.

Survival rates vary according to the stage of the cancer. As with other forms of cancer, survival is highest when the disease is caught early. The ACS reports the survival rates for all stages of oral and oropharyngeal cancer combined as follows:

The five–year survival rate refers to the number of people who will live five years after their cancer is diagnosed. Many people will live much longer than five years, especially if the cancer is detected early and has not spread to the lymph nodes.

Patients with oral cancer are also at greater risk of developing another form of cancer. Newly diagnosed patients have a 15 percent risk of having another cancer in a nearby area, such as the throat or esophagus. In addition, 10 to 40 percent of patients cured of oral or oropharyngeal cancer will develop a second oral cancer or cancer in nearby tissues later in life, according to ACS. Individuals who are diagnosed with oral cancers need to avoid known risk factors (e.g., tobacco use, alcohol) and need to be monitored throughout their lives.