Throat cancers are hard to diagnose early because the symptoms are "not specific," according to Dr. Nishant Agrawal, an otolaryngologist and assistant professor at Johns Hopkins University in Baltimore.
"We all get sore throats and take antibiotics and there is some improvement," Agrawal said. "Patients ignore the symptoms and by the time it has developed in the lymph nodes it's stage three or four. That's when most are diagnosed.
"In general, oropharyngeal cancer is usually involved at the base of the tongue and the tonsils and can be associated with HPV, and even at stage four can have an 80 percent cure rate," he said.
The human papillomavirus, or HPV, is the most common sexually transmitted infection in the United States.
Recent studies have found connections between HPV and cancers of the mouth and throat, and recently with lung cancer. Other HPV-related cancers include vulva, vaginal, penile and anal.
HPV has long been known to result in cancers of the sex organs, particularly the cervix. Doctors say men are more prone to throat cancer after kissing or oral sex with an infected partner.
According to a National Institutes of Health website, use of tobacco or alcohol are among the factors that put people at risk of developing throat cancer. Combining tobacco and drinking increases the risk.
Douglas, who has two children with Catherine Zeta-Jones, said he enjoyed the summer traveling with his family before returning to the doctor.
A biopsy found he had late, stage-four cancer, "which is intense, and so they've had to go at it," he told Letterman.
Stage four means that there is lymph node involvement in the cancer. Unlike a breast cancer that has metastasized, throat cancer at this stage is not as widespread.
Cullen said that doctors likely did not operate because chemotherapy and radiation "work very well" with throat cancers. Removing a tumor at the base of the tongue could lead to speech and swallowing problems.
Others who have been diagnosed with throat cancer are writer Christopher Hitchens, who was diagnosed this summer, former Texas Gov. Ann Richards and the late actor Ron Silver.
Throat cancer forms in the tissues of the pharynx, the hollow tube inside the neck that starts behind the nose and ends at the top of the windpipe and esophagus. It can include cancer of the nasopharynx (the upper part of the throat behind the nose), the oropharynx (the middle part of the pharynx), and the hypopharynx (the bottom part of the pharynx). Cancer of the larynx (voice box) may also be included as a type of throat cancer.
Most throat cancers are squamous cell carcinomas.
According to the National Cancer Institute, there were 12,720 new cases of laryngeal and 12,660 of pharyngeal in 2010. The estimated annual deaths are 3,600 and 2,410, respectively.
Head and neck cancers account for approximately 3 to 5 percent of all cancers in the United States. These cancers are more common in men and in people over age 50.
Risk factors include tobacco and alcohol use: 85 percent of all head and neck cancers are related to smoking and that risk increases with alcohol use.
Some reports have found that people who smoke and drink are up to 100 times more likely to get head and neck cancer than are people with neither habit.
Other risk factors are the human papilloma virus, a group of about 100 different viruses. The 16 and 18 are associated with throat cancer.