Oral Cavity (Mouth) and Oropharyngeal (Throat) Cancer

Almost all cancers in the oral cavity and oropharynx are squamous cell carcinomas, also called squamous cell cancers. These cancers start in squamous cells, which are flat, thin cells that form the lining of the mouth and throat.

• Squamous cell carcinoma in situ: The earliest form of squamous cell cancer is called carcinoma in situ. This means that the cancer cells are only in the epithelium, the top layer of cells lining the oral cavity and oropharynx.
• Invasive squamous cell carcinoma: The cancer is referred to as invasive if the cancer cells have grown past the epithelium and into the deeper layers of the oral cavity or oropharynx.

HPV-related cancers

In the United States, most squamous cell cancers of the oropharynx are caused by infection with certain high-risk types of the human papillomavirus (HPV). This is called HPV-positive cancer.

HPV is rarely associated with oral cavity cancer.

HPV-positive cancers are seen more often in young people with no history of tobacco or alcohol use. These cancers tend to have a better outcome (prognosis) than HPV-negative cancers (squamous cell cancers not related to an HPV infection). This is most likely because HPV-positive cancers shrink more when treated with chemotherapy and radiation. Learn more in Causes, Risk Factors, and Prevention for Oral Cavity and Oropharyngeal Cancers.

Verrucous carcinoma

This is a rare type of squamous cell cancer most often found in the gums and cheeks. It is low-grade (slow growing) and hardly ever spreads to other parts of the body.

These cancers can start in the glands in the lining of the mouth and throat. There are many types of minor salivary gland cancers, including adenoid cystic carcinoma, mucoepidermoid carcinoma, and polymorphous low-grade adenocarcinoma. See Salivary Gland Cancer to learn more about these, as well as benign salivary gland tumors.

The tonsils and base of the tongue contain immune system (lymphoid) tissue, where cancers called lymphomas can start. For more information about these cancers, see Non-Hodgkin Lymphoma (Adults) and Lymphoma in Children.

Smoking and chewing tobacco are the most common causes of leukoplakia and erythroplakia. Poorly fitting dentures that rub against the tongue or the inside of the cheeks can also cause these changes. Sometimes, there is no clear cause.

• Leukoplakia: Most cases of leukoplakia do not turn into cancer. Some leukoplakias are cancer or have pre-cancer changes that can turn into cancer if not properly treated.
• Erythroplakia and erythroleukoplakia: These are less common but usually more serious. Compared to white lesions or leukoplakia, it is more common for red lesions to be cancer or develop into cancer later.

Most oral cancers do not develop from pre-existing leukoplakia or erythroplakia lesions, but a biopsy is the only way to know for certain if one of these lesions has cancer cells or dysplastic (pre-cancer) cells. (See dysplasia, below). Other tests might be done first to help determine if a biopsy is needed or to choose the best area to sample for a biopsy.

Dysplasia is a term used to describe the degree to which cells look abnormal under a microscope. Dysplasia can be categorized as mild, moderate, or severe. Knowing the degree of dysplasia helps predict how likely it is that a lesion will turn into cancer or go away on its own.

For example, severe dysplasia is more likely than mild dysplasia to become cancer. Dysplasia sometimes goes away if the cause is removed, such as poorly fitting dentures.