Oropharyngeal cancer develops in the oropharynx, the middle part of the throat that sits directly behind the mouth. The pharynx is actually a hollow tube about 5 inches long that extends from the area behind the nose to the esophagus. Air and food pass through the pharynx on the way to the windpipe or the esophagus. The oropharynx includes the soft palate (the back of the mouth), the base of the tongue and the tonsils. Cancers of the oral cavity and oropharynx most commonly start in the cells lining these areas (the epithelium).

According to the American Cancer Society (ACS), about 29,800 new cases (20,000 in men and 9,800 in women) of oral cavity and oropharyngeal cancer will be diagnosed in the United States in 1999. Although death rates have been decreasing since the mid-1980s, an estimated 8,100 people (5,400 men and 2,700 women) are expected to die of oral cavity and oropharynx cancer in 1999.

Squamous cells form the lining of the oral cavity and oropharynx. More than 90 percent of cancers of the oral cavity and oropharynx are squamous cell carcinomas, also called squamous cell cancer. The earliest form of this malignancy is called carcinoma in situ, in which the cancer cells are present only in the epithelium, the layer of cells that form the lining. Invasive squamous cell cancer occurs when cancer has spread into deeper layers of the oral cavity or oropharynx.