Michael Douglas told a US television audience on Tuesday night that he has been diagnosed with and is receiving treatment for stage four throat cancer.

Speaking on David Letterman's "Late Show" to promote the release of his new film "Wall Street: Money Never Sleeps", the 65- year old American actor and producer said his doctors had told him he has an 80 per cent chance of survival.

Stage four means the cancer has spread from the primary site, for example to another organ.

His press spokesman Allen Burry said that Douglas is being treated at Manhattan's Memorial Sloan-Kettering Cancer Center:

"The tumor is at the base of his tongue and his doctor's prognosis is for a full recovery," he told ABCNews.com.

In the TV interview Douglas said he was diagnosed earlier in the summer: he had been experiencing a sore throat that would not go away and he consulted several doctors.

When asked about the severity of the tumor, Douglas said "I am above the neck, so nothing's gone down", and that "the expectations are good".

He told Letterman he was a drinker and a smoker and that "this particular type of cancer is caused by alcohol and drinking", reported the New York Times.

Earlier this year, Douglas pleaded with a judge who sentenced his son Cameron Dougals to five years in prison for drug dealing, to exercise leniency because there was a history of drug and alcohol abuse in the family and he himself had received treatment in the 1990s for alcohol abuse.

The actor said he has now completed the first week of an eight-week chemotherapy and radiotherapy treatment, which he described as "very intense".

Apart from revealing the tumor is at stage four, Douglas did not, however, say what type of throat cancer he has, leaving others to speculate on what it might be.

Throat cancer, also called pharyngeal cancer, is a broad term that refers to a range of cancers that form in the tissues of the pharynx, the tube that starts behind the nose and finishes at the top of the windpipe (trachea) and foodpipe (esophagus). Air and food travel through the pharynx to the trachea or the esophagus.

If the cancer started at the tumor at the base of his tongue (that his press representative described), then Douglas probably has oropharyngeal cancer, suggest two head and neck medical experts consulted by WebMD.

Oropharyngeal cancer is cancer of the oropharynx, the middle part of the pharynx, behind the mouth, and includes the back one-third of the tongue, the tonsils, the soft palate, and the side and back walls of the throat.

Most oropharyngeal cancers are squamous cell carcinomas, thin, flat cancer cells that line the inside of the oropharynx.

According to information from the US National Cancer Institute, risk factors for oropharyngeal cancer include smoking and chewing tobacco, heavy alcohol use, a diet low in fruits and vegetables, and being infected with the human papillomavirus (HPV).

Factors affecting chances of recovery usually depend on the stage and grade of the cancer, the location of the tumor, whether it is associated with HPV infection, and the patient's general health.

Another head and neck cancer expert told ABCNews.com that it was important to know if the cancer was HPV related, as these are the ones that respond well to chemo and radiotherapy and have a good prognosis.

"The ones associated with smoking and drinking respond well, but not as well," said Dr Kevin Cullen, director of the University of Maryland Greenebaum Cancer Center.

Cullen said survival rates for throat cancers linked to smoking and drinking are around 50 to 60 per cent and below, whereas those for HPV-related cancers are above the 80 per cent mark.

Related articles:

-- Addition Of Chemotherapy To Radiotherapy Increases Survival For Patients With Advanced Head And Neck Cancer (Oct 2009)

-- Rare Head And Neck Cancer Linked To HPV (Oct 2009)

Sources: ABC News, NCI, WebMD, New York Times, MNT archives.

Written by: Catharine Paddock, PhD